Sum and Difference Identities

Question

Rewrite cos(x+π/4) in terms of sin(x) and cos(x)

Answer 1

Angle addition formula for cosine

 

cos(x)cos(pi/4) - sin(x)sin(pi/4) =

 

sqrt(2)/2 * [cos(x)  - sin(x) ]  <--- cos(45)=sin(45) = sqrt(2)/2 and it factors out