[" Prove the following "],[" 15."cos((pi)/(4)-x)*cos((pi)/(4)-y)-sin((pi)/(4))x]

Prove the following cos ((pi) / (4) -x) cos ((pi) / (4) -y) -sin ((pi) / (4) -x) sin ((pi) / (4) - y) = sin (x + y)

cos((3pi)/4+x)-sin(pi/4-x)=?

Prove the following: cos((3pi)/4+x)-cos((3pi)/4-x)=-sqrt2 sinx

Prove the following: cos(pi/4-x)cos(pi/4-y)-sin(pi/4-x)sin(pi/4-y)= sin (x+ y)

Prove the following: cos(pi/4-x).cos(pi/4-y)-sin(pi/4-x).sin(pi/4-y)=sin(x+y)

Prove the following: (i) cos((3pi)/(4)+x)-cos((3pi)/(4)-x)=-sqrt2 sin x (ii) cos"((pi)/(4)+x)+cos((pi)/(4)-x)=sqrt2 cos x .

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

Prove the following: cos(pi/4+x)+cos(pi/4-x)=sqrt2cosx

Prove that: cos((pi)/(4)-x)cos((pi)/(4)-y)-sin((pi)/(4)-x)sin((pi)/(4)-y)=sin(x+y)

Prove that cos((pi)/(4)-x)cos((pi)/(4)-y)-sin((pi)/(4)-x)sin((pi)/(4)-y)=sin(x+y)