1/2cosX-根号3/2sinX
=sin30cosX-cos30sinX
=sin(30-X)
根号2（sinX-cosX）
=2*(sinXcos45-cosXsin45)
=2sin(X-45)
根号2/4sin(π/4-X)+根号6/4cos(π/4-X)
=根号2/8*[sin(π/4-X)cos60+cos(π/4-X)sin60]
=根号2/8*sin(7π/12-X)
sin164°sin224°+sin254°sin314°
=(cos(164-224)-cos(164+224))/2+
(cos(254-314)-cos(254+314))/2
=(cos60-cos28)/2+(cos60+cos28)/2
=cos60
=1/2