Question

cos(81+theta)=sin(9-theta)

Answer 1

Cos(81+theeta)
Sin(90-81-theeta)
Sin(9-theeta)
= rhs

Answer 2

cos(theta) can be written as c sin(90-theta)
similarly,cos(81+theta)=sin(9o-(81+theta)
=cos(81+theta)=sin(90-81-theta)
=cos(81+theta)=sin(9-theta)