Question

Rewrite the given expression in terms of the sum or difference of 2 angles. sin(pi/7)cos(pi/2)+cos(pi/7)sin(pi/2)
a. cos (pi/7-pi/2)
b. cos (pi/7+pi/2)
c. sin (pi/7-pi/2)
d. sin (pi/7+pi/2)

Answer 1

Do you know the sum and difference identities for sine and cosine?

Answer 2

This will help, they are in the 2nd section, "Angle-Sum and -Difference Identities"

http://www.purplemath.com/modules/idents.htm

Answer 3

thank you!!