sin105°
= sin(45°+60°)
= sin45°cos60°+cos45°sin60°
= √2/2*½+√2/2*√3/2
= √2/4+√6/4
= (√2+√6)/4
sin75°
= sin(45°+30°)
= sin45°cos30°+cos45°sin30°
= √2/2*√3/2+√2/2*½
= (√2+√6)/4
sin15°
= sin(45°-30°)
= sin45°cos30°-cos45°sin30°
= √2/2*√3/2-√2/2*½
=(√6-√2)/4