Find the exact value of the expression: sin20\deg cos\deg +cos20\deg sin40\deg =

Answer 1

Observe that, for any a and b,

sin(a+b) = cos(a)sin(b) + sin(b)cos(a)

Use this with a = 20 degrees and b = 40 degrees to find

sin(60) = sqrt(3)/2 = cos(20) sin(40) + sin(20) cos(40).