这是一个公式.可以利用和差角公式进行证明,
(1/2)(cos2B-cos2A)
=(1/2){cos[(A+B)-(A-B)]-cos[(A+B)+(A-B)]}
=(1/2)[cos(A+B)cos(A-B)+sin(A+B)sin(A-B)]
-(1/2)[cos(A+B)cos(A-B)-sin(A+B)sin(A-B)]
=(1/2)sin(A+B)sin(A-B)+(1/2)sin(A+B)sin(A-B)
=sin(A+B)sin(A-B)
这是一个公式.可以利用和差角公式进行证明,
(1/2)(cos2B-cos2A)
=(1/2){cos[(A+B)-(A-B)]-cos[(A+B)+(A-B)]}
=(1/2)[cos(A+B)cos(A-B)+sin(A+B)sin(A-B)]
-(1/2)[cos(A+B)cos(A-B)-sin(A+B)sin(A-B)]
=(1/2)sin(A+B)sin(A-B)+(1/2)sin(A+B)sin(A-B)
=sin(A+B)sin(A-B)