Question

Write the expression as either the sine, cosine, or tangent of a single angle.
cos pi/3 cos pi/5 + sin pi/3 sin pi/5

Answer 1

use the identity:
cos (a-b)=cos a cos b +sin a sin b

Answer 2

but how do u use that to solve it

Answer 3

in this case you have a=pi/3 and b=pi/5 lets say
then cos pi/3 cos pi/5 + sin pi/3 sin pi/5=cos (pi/3 - pi/5)=cos (-2pi/15)=cos(2pi/15)
you could've different answers due to periodicity..but all are same in numeric value

Answer 4

thank you

Answer 5

my pleasure