证明sina*sinb=[cos(a-b)-cos(a+b)]/2
问题描述:
证明sina*sinb=[cos(a-b)-cos(a+b)]/2
答
cos(a-b)=cosacosb+sinasinb(1)
cos(a+b)=cosacosb-sinasinb(2)
(1)-(2)
cos(a-b)-cos(a+b)=2sinasinb
sinasinb=[cos(a-b)-cos(a+b)]/2