如果是 π/6,你就对了
根3cos派/12-sin派/12
=2(根3/2*cos派/12-1/2*sin派/12)
=2(cosπ/6*cosπ/12-sinπ/6*sinπ/12)
=2cos(π/6+π/12)
=2cosπ/4
=√2