calculus
posted by Molly .
y = (sin x) / (1 + tan x)

Is there a question here?

Sorry
y'= 
just use the quotient rule. If
y = u/v
y' = (vu'uv')/v^2
y' = [(1+tanx)(cosx)  (sinx)(sec^2 x)]/(1+tanx)^2
= ((cosx  (sinx)(tan^2 x))/(1+tanx)^2