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Started by Legend, Aug 26, 2014, 12:55 AM

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Xevross

I know something you don't?  :o
I'll explain!
So basically first we learned about partial derivatives, a derivative with respect to another.  u = f(x,y,z).  The way we take the derivative in this case is by treating the other values as if they were a constant.  So if we had z = xy + y + x,  if we took the derivative with respect to y, we would treat x as a constant.  dz/dy = x+1, so we pretend that x is a constant.  d/dy (xy)=x is the same thing as d/dy (3y) = 3.   We also get the dz/dx = y+1.

The double integrals are generally used for volume, sometimes they are used for areas.  Basically it's kinda, but not exactly the opposite of that.  z= f(x,y), basically you take two integrals, one for y, and one for x.  And you keep the other variable as a constant.  
There are some cases, where the inside integral will have a function of the outer.  That case you plug in the function for the variable you are integrating. Sometimes you have to switch the outer and inner integrals and you also have to switch the bounds of the integral. I understand how to do this, but I keep having troubles getting the right answer.  :P
Sounds pretty interesting! I'm sure I'll learn that at university ;)

Why do you have to change the bounds?