use the equations cos(theta)=0.5(exp(i.theta)+exp(-i.theta)) and sin(theta)=0.5i(exp(i.theta)-exp(-i.theta)) to show that:

sin(theta-y)=sin(theta)cosy-sinycos(theta) and cos(tetha+y)=cos(theta)cosy - sin(theta)siny

Sorry about the symbols im not sure how to insert them

Please help, would be ever so greatful