Posted by **sarah** on Saturday, March 21, 2009 at 5:20pm.

Hi could someone please explain to me how i would use the chain rule

dy/dx = dy/du(du/dx) to solve for

y= sin(x+y) - im looking for dy/dx

i don't understand the steps

thanks

- math calculus -
**Reiny**, Saturday, March 21, 2009 at 5:52pm
let u = x + y

du/dx = 1 + dy/dx

then y = sin u

and dy/dx = cosu du/dx

= cosu (1 + dy/dx)

= cosu + dy/dxcosu

dy/dx - dy/dxcoxu = cosu

dy/dx = cosu/(1 - cosu)

= cos(x+y)/( 1 - cos(x+y)

personally I would bypass all that subbing and my second line would be

dy/dx = cos(x+y)(1 + dy/dx)

etc.

- math calculus -
**sarah**, Saturday, March 21, 2009 at 9:18pm
alright, but i dont know how i would now isolate for dy/dx?

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