Question

if cos(40 degree+theta)=sin 30 degree,find theta

Answer 1

cos(40 + θ ) = sin 30 

cos(40 + θ ) = cos 60

40 + θ          = 60 

θ                  = 20 

Answer 2

cos (40°+theta)=sin 30°
cos (40°+theta)=sin (90°-60°)
cos (40°+theta)=cos 60°
40°+theta=60°
theta=60°-40°
theta=20°