-
Hey Guest. Check out your NeoGAF Wrapped 2025 results here!
The Math Help Thread
- Thread starter -COOLIO-
- Start date
- Status
Okay guys here we go. Kudos to anyone who can do this.
If you can help with it please also explain.
I'm not 100% sure if this is right, but here goes
Sorry for the terrible quality
I'm not 100% sure if this is right, but here goes
Sorry for the terrible quality
Looks good. Thanks for that, give me a few minuets to look that over.
krameriffic
Member
It looks right, but since the problem statement is an "if and only if", you should probably work it the other direction. My math professors always grilled me for not doing that on if and only if proofs.
The part that bothers me "if and only if". I don't know how to prove this is the only way for f/|f| to be constant. I can kind of see that it's the only way for (f'•f) to reduce to (f•f), but I don't know how to explain it mathematically.
edit: yeeaaah ... good luck
edit2:
Something ... something ... identities ... I dunno
edit: yeeaaah ... good luck
edit2:
Something ... something ... identities ... I dunno
The Last Wizard
Member
How do I find the domain and range of this?
g(x) = x^2 − 2
g(x) = x^2 − 2
What values can you plug into x and produce real numbers? What are the values of y can you get?
I think it's all real numbers for x, and - 2 to infinity for the range.
The Last Wizard
Member
so it was (-infinity,infinity) for x and for y it was [-2,infinity).
I thought the way to do the problem was that the answer would be whatever number that gives you 0 when plugged in.
The Last Wizard
Member
what's a kernel? I think I might've been taught using a different word for it.
Pretty funny that I'm getting asian dating site ads in this thread.
TimesEunuch
Member
Factor out the (f.f)^{-1/2}. So g' = (f.f)^{-1/2}(f' - (f.f')(f.f)^{-1/2} f). So if g'=0, then f' = (f.f')(f.f)^{-1/2} f, and lambda=(f.f')(f.f)^{-1/2} works as your function.The part that bothers me "if and only if". I don't know how to prove this is the only way for f/|f| to be constant. I can kind of see that it's the only way for (f'f) to reduce to (ff), but I don't know how to explain it mathematically.
edit: yeeaaah ... good luck
edit2:
Something ... something ... identities ... I dunno
BTW the hint in the original question seems kind of misleading to me.
Thanks for the help guys, the teacher I have for this class is honestly the worst that I have ever had. She doesn't return Emails, she doesn't even know what is in our homework.
I have a few more problems that I need help with, but before I do what books could I buy to help with my Differential Geometry class? The one my teacher has us using is crap. She said that she chose this one to "save us money." I appreciate the sentiment, I really do, but with it being our last semester I think we can sacrifice another $80 to get the most out of the class.
I have a few more problems that I need help with, but before I do what books could I buy to help with my Differential Geometry class? The one my teacher has us using is crap. She said that she chose this one to "save us money." I appreciate the sentiment, I really do, but with it being our last semester I think we can sacrifice another $80 to get the most out of the class.
ThLunarian
Member
I could really use some resources to better understand the material in my Operations Management class. It's using a lot of statistics, and I haven't taken a Stats class in 10 years, and English isn't the teacher's first language.
Right now, we're using Critical Paths and standard normal distributions to determine how likely it is that a task will be completed in X number of days. I don't really have a specific question because the material still seems to be over my head. There are a lot of symbols involved whose meanings don't make sense to me, especially the Greek letter parts.
So... is there something that I can read or watch that might help me understand better? Thanks.
Right now, we're using Critical Paths and standard normal distributions to determine how likely it is that a task will be completed in X number of days. I don't really have a specific question because the material still seems to be over my head. There are a lot of symbols involved whose meanings don't make sense to me, especially the Greek letter parts.
So... is there something that I can read or watch that might help me understand better? Thanks.
dinazimmerman
Incurious Bastard
"zero locus" is a cool name for it too. =)
mohsinkhan
Member
To be completely honest, I went through engineering we did alot of this stuff, before spending money I recommend just looking around the Internet, most things are on their,
SniperHunter
Banned
Can you guys recommend me a good graphic calculator? I don't spend $150 on one. I am getting sick of drawing graphs bad hand then procrastination and never checking my work.
mohsinkhan
Member
I would recommend a TI-83 or TI-84, but before you buy make sure you can use one in class, most classes don't allow then during exams.
SniperHunter
Banned
It's not about the exam, I need to to see what I am doing, I need to understand...that's why I need one. I still don't understand how to draw a graph of y=xsinx, the amplitude increase but how? Can you tell me?
The maximum value of y=sinx is 1 at the peaks, so y=xsinx is x at the peaks. If take the y=xsinx graph and draw y=x on it you can see the peaks all hit y=x.
If you work at a computer or with a smartphone Wolfram Alpha will do as good a job as a calculator.
mohsinkhan
Member
Look at f0rk's post, math is not being able to solve a specific problem, but you must be able to develop a robust methodical approach to any problem, if you can plot y=x you should be able to plot y=xsinx.
SniperHunter
Banned
all right i will keep that in mind, thnx
ChuyMasta
Member
Okay guys here we go. Kudos to anyone who can do this.
If you can help with it please also explain.
DAMN. Could someone EXPLAIN the question. I don't even know what half the symbols MEAN.
Double vertical lines? R raised to the nth power? Weird looking C? Scalar? Some greek letters? Right pointing arrow?
I've spent the last year on a placement for a bank that was definitely productive, but I'm scared I'm going to have forgotten how to do proper maths like that when I return for my final year lol.
krameriffic
Member
f is bolded because it's a vector function mapping ordered pairs of the form (a,b) into R^n. The stroked R stands for the set of all real numbers, and the nth power denotes the dimensionality of the set/space. The script C^2 stands for twice continuous and differentiable, which is mathematical jargon for it being an ordinary function. ||f|| is the magnitude or length of the vector function f, and itself is a scalar. The lambda is just used as a general scalar function.
Yeah, I'll start doing that more definitely.
Help with another problem, pls.
Just like last time, I can show that under these conditions, the statement is true. But I can't prove these are the ONLY conditions when the the statement is true. I also did a terrible job presenting the "proof", but I hope it helps.
Thanks. I feel really stupid but I see it now. I just needed to rearrange so that:
f' = [ (f'.f) / (f.f) ] f
The dot product results in a scalar, so the part in square brackets is a scalar function.
Therefore f' = lambda f
Just make sure you understand all the basic laws and definitions, and then do alot of practice problems. Proofs are tough because you need magically envision the path to the solution. At first, it takes hours of trying different things and having sudden realizations until you figure it out. But with some practice you get faster at it. Textbooks can't really teach you that.
I mean, just look at the above problem. I had trouble envisioning the path to the solution, because I didn't realize what I was looking at. So I need more practice too
TimesEunuch
Member
The trick for the reverse implication is to express alpha'', alpha' and alpha in terms of (lambda alpha)'', (lambda alpha)' and lambda alpha. So for exampleJust like last time, I can show that under these conditions, the statement is true. But I can't prove these are the ONLY conditions when the the statement is true. I also did a terrible job presenting the "proof", but I hope it helps.
alpha'' = [1/lambda](lambda alpha)'' - [2 lambda'/lambda^2] (lambda alpha)' + [(2 lambda'^2-lambda lambda'')/lambda^3] (lambda alpha)
(be sure to check my algebra, though). Notice, the nonvanishing of lambda is important here. Then take c_1 alpha + c_2 alpha' + c_3 alpha''=0, write in terms of lambda alpha, (lambda alpha)' and (lambda alpha)'', and use the fact that the latter three are linearly independent.
If you're just covering differential geometry of curves and surfaces, I learned from Millman and Parker, and remember it being pretty good. That was a while ago, though. A lot of people like do Carmo, but I've never used it. For more advanced differential geometry, Lee is one of the clearest texts I've looked at (there's now a second edition). His other texts look good too, though I haven't used them much.Troll said:
One final note - if you know some LaTeX, you would probably get a quicker response to your questions by asking them on http://math.stackexchange.com
Thanks, that made alot of sense. I expressed (La), (La)' and (La)'' in terms of a, a' and a'', and then plugged into k1(La) + k2(La)' + k3(La)'' = 0. But I should have expressed a, a' and a'' in terms of (La), (La)' and (La)'', and then plugged into c1 a + c2 a' + c3 a'' = 0. The algebra is messier but I got the same expression for a'' as you.
I swear I used to be pretty good at this stuff lol. I'm so out of shape.
Mathematical statistics, but this is probably the best place to ask.
Would appreciate it if someone could help me with this.
We need to implement a rule that you have to show your work first
Do you know how to find the conditional distribution of X1 given that X2 = -1? There's a specific method to solving it. Then it's just a matter of knowing some properties.
Let Y = X1 - X3
E(Y) = E(X1) - E(X3)
var(Y) = var(X1) + var(X2) - 2cov(X1,X2)
cov(Y,X2) = cov(X1,X2) - cov(X3,X2)
oxrock
Gravity is a myth, the Earth SUCKS!
I'm working on a problem with transforming functions. I'm really unsure of what I'm doing here so I'm hoping you guys can check my work on this problem.
Problem: F(x) = sqrt (x)
g(x) = 2 sqrt (x+1) -1
sqrt (x) coords [0,0] [1,1] [4.2] [9,3]
My work
1) [-1,0] [0,1] [3,2] [8,3]
2) [-1,0] [0,2] [3,4] [8,6]
3) {-1,-1] [0,1] [3,3] [8,5]
input/help received is much appreciated. If there's essential information missing or any other stupid mistake on my part, please feel free to speak up.
Problem: F(x) = sqrt (x)
g(x) = 2 sqrt (x+1) -1
sqrt (x) coords [0,0] [1,1] [4.2] [9,3]
My work
1) [-1,0] [0,1] [3,2] [8,3]
2) [-1,0] [0,2] [3,4] [8,6]
3) {-1,-1] [0,1] [3,3] [8,5]
input/help received is much appreciated. If there's essential information missing or any other stupid mistake on my part, please feel free to speak up.
SniperHunter
Banned
I found pre-calculus harder than calculus & vectors (high school). With calculus make sure to get good at finding derivatives, practice, practice and practice some more!
save this link
http://www.math.ucdavis.edu/~kouba/ProblemsList.html
EDIT: nvm, got it. complex analysis is not going to be kind to me.
bleh, hate when this happens. got through the first 9 problems on my analysis hwk breezily, last one is throwing me for a loop either because I'm math-ed out or because it's straight-up confusing.
for reference, 1 is:
bleh, hate when this happens. got through the first 9 problems on my analysis hwk breezily, last one is throwing me for a loop either because I'm math-ed out or because it's straight-up confusing.
for reference, 1 is:
All looks good to me. easiest way to check of course is to plug your new coordinates into g(x) and make sure they're correct
EDIT: nvm, got it. complex analysis is not going to be kind to me.
bleh, hate when this happens. got through the first 9 problems on my analysis hwk breezily, last one is throwing me for a loop either because I'm math-ed out or because it's straight-up confusing.
for reference, 1 is:
All looks good to me. easiest way to check of course is to plug your new coordinates into g(x) and make sure they're correct
you could just set a to be one of the n nth roots to 1, and let b = 1. Use the identity given in problem 1 and everything follows easily.
You could let a = z and b = 1, multiply the equation you're supposed to solve with (z-1), let z != 1 and show that it transforms the equation into z^n - 1^n. It's the opposite approach, but works just as well.
Additionally: Studying complex analysis is a privilege. Make sure you appreciate the beauty of it.
Sweet, exactly what I did. I just hadn't read the text closely enough to understand the e^(2pi*i) term.you could just set a to be one of the n nth roots to 1, and let b = 1. Use the identity given in problem 1 and everything follows easily.
You could let a = z and b = 1, multiply the equation you're supposed to solve with (z-1), let z != 1 and show that it transforms the equation into z^n - 1^n. It's the opposite approach, but works just as well.
Additionally: Studying complex analysis is a privilege. Make sure you appreciate the beauty of it.
I can't believe how great you guys are, seriously. Thanks for all your help on this!
This should be the last one for me for a while, in my five classes these are the last things that I have problems with. When I get a chance, I will look over the thread and help out too. I want to pull my weight in this thread when I can.
First this one
Then this is a separate problem. 12 and 13 are giving me fits.
This should be the last one for me for a while, in my five classes these are the last things that I have problems with. When I get a chance, I will look over the thread and help out too. I want to pull my weight in this thread when I can.
First this one
Then this is a separate problem. 12 and 13 are giving me fits.
oxrock
Gravity is a myth, the Earth SUCKS!
First off, some of the things you guys are posting in here is going to make my brain explode when I get to them =(
Secondly, I need uber math gaf to come to the rescue yet again. I'm sensing a trend here. The current problem is composite functions. here's the problem I'm working on:
F(x) = 4 - x, G(x) = 2x^2 +x +5
The question is broke down into A,B,C where I have to find (FoG)(x), (GoF)(x), and (FoG)(2)
A and C are not the concern however, I don't really know why I'm even adding them. B however I'm having troubles with.
Here's my work for B:
2(4-x)^2 +(4-x)+5
2(16-x^2) +9 -x
32 -2x^2 +9 -x
-2x^2 -x +41
The book shows the answer as this :
If someone could explain to me the error of my ways, I'd be extremely grateful.
Secondly, I need uber math gaf to come to the rescue yet again. I'm sensing a trend here. The current problem is composite functions. here's the problem I'm working on:
F(x) = 4 - x, G(x) = 2x^2 +x +5
The question is broke down into A,B,C where I have to find (FoG)(x), (GoF)(x), and (FoG)(2)
A and C are not the concern however, I don't really know why I'm even adding them. B however I'm having troubles with.
Here's my work for B:
2(4-x)^2 +(4-x)+5
2(16-x^2) +9 -x
32 -2x^2 +9 -x
-2x^2 -x +41
The book shows the answer as this :
2x^2 -17x +41
(4-x)^2 is not (16-x^2). FOIL, son!
talisayNon
Member
Can someone explain to me how to do semantic security proofs?
I have to prove why a substitution cypher is semantically secure using that Adversary game that you have to play. I have no idea where to start.
I have to prove why a substitution cypher is semantically secure using that Adversary game that you have to play. I have no idea where to start.
oxrock
Gravity is a myth, the Earth SUCKS!
what a derp moment on my part, thanks
Himynameischris
Member
Hey gaf, full disclosure this isn't for me it's for a friend but she's having a really hard time understanding how to do these.
0.66P/240,000 = 0.66*(P-145,600)/110,000
P = 2.18*(P-145,600)
P = $317,673
Online answer is $268,800
can anyone explain the steps to this? Thanks a bunch
0.66P/240,000 = 0.66*(P-145,600)/110,000
P = 2.18*(P-145,600)
P = $317,673
Online answer is $268,800
can anyone explain the steps to this? Thanks a bunch
hemtae
Member
After you second step, from the distributive rule you get P=2.18*P - 317673
Subtracting P from both sides you get 0=1.18P - 317673
So 317673/1.18 = ~268800
youngwerther
Banned
Any chemistry people still awake who want to help me out?
We can ask chemistry stuff in here right?
We're having our first test tomorrow and it's mostly over stoichiometry and I'm boned.
I'm running through some practice problems and I'd say I confidently know how to do half of them.
Other times I'll think I know a way but am not sure.
Here is one such problem -
"When 20.0g of C2H6 and 60.0g O2 react to form CO2 and H20, how many grams of water are formed?"
Ok, so I'm guessing the first thing I need to do is balance the equation so that I know the molar ratio between the reactants and the products, right?
So the balanced equation would be
2 C2H6 + 7 O2 -> 4 CO2 + 6 H20
(Sorry, don't know how to type in subscripts)
Soooo, where do I go from there?
I would say -
Properties of Exponents
Rationalizing Denominators
Rational Exponents
Simplifying/Factoring Polynomials (remember to brush up on difference/sum of two cubes)
Rational Expressions
Quadratic Equations
Radical Equations
Interval Notation
Inequalities
Coordinate Plane, Slope
If you brush up on that stuff you should be good to go
We can ask chemistry stuff in here right?
We're having our first test tomorrow and it's mostly over stoichiometry and I'm boned.
I'm running through some practice problems and I'd say I confidently know how to do half of them.
Other times I'll think I know a way but am not sure.
Here is one such problem -
"When 20.0g of C2H6 and 60.0g O2 react to form CO2 and H20, how many grams of water are formed?"
Ok, so I'm guessing the first thing I need to do is balance the equation so that I know the molar ratio between the reactants and the products, right?
So the balanced equation would be
2 C2H6 + 7 O2 -> 4 CO2 + 6 H20
(Sorry, don't know how to type in subscripts)
Soooo, where do I go from there?
Kod1ak said:
I would say -
Properties of Exponents
Rationalizing Denominators
Rational Exponents
Simplifying/Factoring Polynomials (remember to brush up on difference/sum of two cubes)
Rational Expressions
Quadratic Equations
Radical Equations
Interval Notation
Inequalities
Coordinate Plane, Slope
If you brush up on that stuff you should be good to go
Khan Academy is pretty good for most everything, but I don't know for sure if that's exactly what you're looking for. Just searching stuff on Wolfram Alpha or looking at their Examples might help too.
Man, I am really rusty on chem but seeing as no one is in here I'll try and help you until someone comes in and corrects me:
I believe that from here you convert the 20.0g or C2H6 and the 60.0g of O2 to moles. From there you need to figure out what the limiting reactant is. Take however many moles of C2H6 you have and use the ratios from the balanced equation to figure out 1) how many moles of O2 would be required to completely react 2) how many moles of H2O you would obtain.
If the number of moles of O2 needed to completely react is less than the number of moles you get from 60.0g of O2, then C2H6 is the limiting reactant and the number of moles of H2O you obtained above is the answer (well, converted to grams it's the answer).
If the number of moles of O2 needed to completely react is more than the number of moles you get from 60.0g of O2, then O2 is the limiting reactant. Then, you use the number of moles of O2 that you have from 60.0g of O2 and use the ratios from the balanced equation to find how many moles of H2O you would obtain. Convert to grams and you have your answer.
Again, I'm really rusty at chem and the way I phrased this is likely not spot-on, but I do think I've the framework there.
Himynameischris
Member
Oh thanks! that helped her a lot
youngwerther
Banned
Thanks, hours later I finally did this bastard and have a much better understanding of how to solve similar problems.
In case you were dying to know, O2 was the limiting reagent, there was an excess of 3.89 grams of C2H6 , and 28.9 grams of water were produced.
Now to just do several more to make sure I got it down. And then onwards to other types of problems I've forgotten how to do because I was learning this one! Another pot of coffee beckons..
Perhaps I'll be so well prepared for the test that I sleep right through it!!
youngwerther
Banned
I've got another one for anyone who wants to take a stab.
"A solution is prepared by dissolving 14.35 grams of sodium carbonate into water to prepare a total volume of 750.mL. A 150.mL volume of this solution is diluted with water to yield a new volume of 0.600L. What is the concentration of the dilute sodium carbonate solution?"
This type of problem is pretty much my final hurdle because I don't remember going over this in class. We did the very basic M(a)V(a)=M(b)V(b), but that doesn't yield the correct answer here (even after making sure the units are uniform).
I already know the correct answer is 4.53x10^-2 M, I just don't know how to get it. Any help will be appreciated.
"A solution is prepared by dissolving 14.35 grams of sodium carbonate into water to prepare a total volume of 750.mL. A 150.mL volume of this solution is diluted with water to yield a new volume of 0.600L. What is the concentration of the dilute sodium carbonate solution?"
This type of problem is pretty much my final hurdle because I don't remember going over this in class. We did the very basic M(a)V(a)=M(b)V(b), but that doesn't yield the correct answer here (even after making sure the units are uniform).
I already know the correct answer is 4.53x10^-2 M, I just don't know how to get it. Any help will be appreciated.
- Status