π=180°π/12=180°÷12=15°所以sinπ/12=sin15°=sin(45°-30°)=sin45°cos30°-cos45°sin30°=√2/2 ×√3/2-√2/2×1/2=(√6-√2)/4
sinπ/12=sin180/12=sin15°=sin30°/2=√((1+cos30°)/2)=√((1+√3/2)/2)=√(2+√3)/2
