Question

Find dy/dx if y=cos(x+y)

Answer 1

y'  = - sin(x+y) (1+y')

y' [1 + sin(x+y) ] =  - sin(x+y)

y' = - sin(x+y) / [ 1 + sin(x+y) ]  = - 1 + 1/[1 + sin (x+y) ]

y' =  - 1 + 1/[1 + √(1-y²) ]