Can someone check/verify my answer?

Write the expression as either the sine, cosine, or tangent of a single angle.

sin(pi/2)cos(pi/7)+cos(pi/2)sin(pi/7)

My work:
cos(A-B) = cos A cos B + sin A sin B

A = pi/2
B = pi/7

cos(pi/2-pi/7)=2pi/14

Question

Can someone check/verify my answer?

Write the expression as either the sine, cosine, or tangent of a single angle.

sin(pi/2)cos(pi/7)+cos(pi/2)sin(pi/7)

My work:
cos(A-B) = cos A cos B + sin A sin B

A = pi/2
B = pi/7

cos(pi/2-pi/7)=2pi/14

psymon · Answer

Looks like you picked the wrong identity. sinAcosB + sinBcosA is the sum of sines formula.

anonymous · Answer

ohhhh so I should use the sin one then.

psymon · Answer

Yep yep. So same angles, but sin and addition.

anonymous · Answer

Okay so:
sinAcosB+sinBcosA=sin(A+B)
A=pi/2
B=pi/7
sin(pi/2)cos(pi/7)+cos(pi/2)sin(pi/7) = sin 9pi/14

psymon · Answer

Yep, looks good to me.

anonymous · Answer

Yay! Thanks!

psymon · Answer

Sure ^_^