# Is this trigonometric solution correct?

1. Aug 25, 2013

### mileena

1. The problem statement, all variables and given/known data

Solve for y':

4[(cos x)(cos y)(y') + (sin y)(-sin x)] = 0

2. Relevant equations

none

3. The attempt at a solution

4[(cos x)(cos y)(y') + (sin y)(-sin x)] = 0

4y' (cos x) (cos y) - 4 (sin x) (sin y) = 0

4y' (cos x) (cos y) = 4 (sin x) (sin y)

y' = [4 (sin x) (sin y)] / [4 (cos x) (cos y)]

y' = (sin x sin y) / (cos x cos y)

Thanks! I am really shaky at trigonometry, so the above worries me.

2. Aug 25, 2013

### rock.freak667

Yes that is correct. If you want to, you can simplify it even more using the fact that sinA/cosA = tanA.

3. Aug 25, 2013

### mileena

Thanks rock.freak667! See what I mean? I didn't even see that in the equation, although I do know that tan x = sin x/cos x.