Also, while I'm hear, another partial differentiation question
I need to find all the second derivatives for this business
v = e^(xe^y)
To get the first derivatives, I just took the natural log of both sides, followed through with implicit differentiation, and subbed back in v.
So vx = e^(xe^y)e^y
and
vy = e^(xe^y)(xe^y)
Now I need vxx, vxy, vyx, and vyy
I can get vxx easily enough, but the other ones I'm unsure of. Should I start by taking the ln again and using the product properties of logs to get a sum?
In general, the derivative of an exponential function:
d/dx e^u = e^u
du/dx
So you repeat the function and then multiply it by the derivative of the function in the exponent.
First partial with respect to x
dv/dx = e^(xe^y) e^y = e^(xe^

+y
What's going on here? Well, first you know d/dx e^(xe^y) = e^(xe^y) * d/dx xe^y. e^y is a constant, x is a variable. Take the constant out, differentiate x to 1, you get e^(xe^y) * (1) e^y = e^(xe^y)e^y. Sum the exponents because you have like bases.
Second partial XX:
dv^2/dxdx = e^(xe^

+y) e^y = e^(xe^

+2y)
Second partial cross:
Here we switch and treat y as the variable and x as the constant.
dv^2/dxdy = e^(xe^

+y) (xe^

+ 1)
(Remember that cross partials are the same* regardless if you do dxdy or dydx * in most functions you're dealing with--all continuous functions IIRC)
First partial with respect to y
dv/dy = e^(xe^

) (xe^

) = e^(xe^

+ y) (x)
Second partial YY:
dv^2/dydy = e^(xe^

+y) (xe^y + 1) (x)
Why does (x) stick around? It's a constant here, so we can take it out before differentiating.
Because this is a mess, here's everything cleaned up:
You do not need any kind of natural logging. The derivative of e^x is e^x dx. So the derivative of, say, e^(4x) = e^(4x) d/dx (4x) = 4e^(4x). With partials, you treat the variable you are not differentiating with respect to as a constant and the one you are as a variable. So d/dx e^(xy) = e^(xy) d/dx(xy) = e^(xy) y. d/dy e^(xy) = e^(xy) d/dy(xy) = e^(xy) x. In general with
e^ functions, continued differentiation just gets a longer and longer equation, the original equation will still be there.
Learning partial derivatives.
Can anyone help me with this one?
f(x,y) = sin(xcosy)
I know the answer but I don't know how they got it.
For fx, to me it looked like a chain rule problem with a product rule on the inside.
fx = (cosy - xsiny)cos(xcosy).
Apparently I'm way off. Any help?
du/dx sin(u) = cos(u) du/dx
u = xcosy
du/dx sin(u) = cos(xcosy) cos

Why?
d/dx xcos

= cos

d/dx x <-- cos

is a constant, take it out before you differentiate.
Not really a help question, but just kind of a planning one.
Should I take Linear Algebra right after I take Calc I?
I just don't want to end up taking Linear Algebra 2 years from now and forget everything from Calc and/or Discrete.
To your question, it doesn't matter. Linear Algebra I is very separate from Calc I-III. There are no real topics common to both. I also didn't end up using Linear Algebra in my CS degree at all until I got to a few of the upper division specialization courses You should definitely consider doing more math than is required for your program, though. Calc II and Calc III especially. When you get to upper division CS courses, particularly if you do image processing or any kind of low-level processor stuff that requires signals analysis, you'll be very happy if you go to Calc III and beyond.
Well, it's not really so much this one specific question, but all of them. I'm having trouble doing starting proofs in general.
But here's the first question, supposed to be done by direct proof.
For all x in the real numbers, if 0 < x - 2, then 3 < 2x.
So I started with the "Let x be in the real numbers" and "Assume 0 < x-2" and then I just get stuck messing around with "0 < x-2" and "0 < 1" trying to find some way to use transitivity to get 3 < 2x.
I don't know what you're permitted to use in proofs in terms of properties of elementary operators or numbers.
Assume 0 < x - 2 -- Given in problem
Therefor 2 < x-2+2 (Add two to both sizes, 2 < x, property of addition)
Therefor 4 < 2x (Multiple both sides by two, 2(2) < 2(x), property of positive multiplication)
Therefor 3 < 2x-1 (Subtract one from both sides, property of subtraction)
2x-1 < 2x for all x (Property of subtraction)
3 < 2x -1 < 2x so by transitivity 3<2x