Sin 5/12 phi cos 1/12 phi

TriGonoMetRi

sin a cos b = 1/2 (sin (a + b) + sin (a - b))

π = 180°

•••
sin (5/12 π) cos (1/12 π)
= 1/2 (sin (6/12 π) + sin (4/12 π))
= 1/2 (sin (1/2 π) + sin (1/3 π))
= 1/2 (sin 90° + sin 60°)
= 1/2 (1 + 1/2 √3)
= 1/2 + 1/4 √3 ✔