sin 5/12π
=sin(1/6π +1/4π)
=sin(1/6π)cos(1/4π) + cos(1/6π)sin(1/4π)
=√2/2*1/2 + √2/2*√3/2
=(√2+√6)/4
cos 5/12π
=cos(1/6π +1/4π)
=cos(1/6π)cos(1/4π) — sin(1/6π)sin(1/4π)
=√3/2*√2/2 — 1/2 *√2/2
=(√6 — √2)/4