Feel help: Need math help? - Help.com

a donut has one surface and so does a ball.

Rico wrote:
This one has been giving me a headache.

4xy + 1 + (2×2 + cos y)y’ = 0

fx(x,y) = 4xy + 1 and fy(x,y) = 2×2 + cos y

Integrate the first equation with respect to x to get

f(x,y) = 2×2y + x + C(y) Notice since y is treated as a constant we write C(y).

Take the partial derivative with respect to y to get

fy(x,y) = 2×2 + C’(y)

We have two formulae for fy(x,y) so we can set them equal to each other.

2×2 + cos y = 2×2 + C’(y)

C’(y) = cos y

C(y) = sin y

f(x,y) = 2×2y + x + sin y

So the solution is:

2×2y + x + sin y = C

I solved it in my head. ;p