Question

Cos(90-theta) × sin(90-theta) is equal to tan theta / 1+ tan theta

Answer 1

sin(theta)=cos(90-theta) similarly cos sin(90-theta)
Cos(90-theta) × sin(90-theta) =sin(theta)×cos(theta) =k let theta=x
k=sin(x) . cos(x)
k= cos x . cos x .tanx
k= cos^2 ( x ) .tan(x) = tanx /sec^2 (x) =tan(x) / 1+tan^2 x