cos(a-b/2)=-1/9 sin(a/2-b)=2/3 且π/2

问题描述:

cos(a-b/2)=-1/9 sin(a/2-b)=2/3 且π/2
cos(a-b/2)=-1/9 sin(a/2-b)=2/3 且 π/2

cos[(a+b)/2]=cos[(a-b/2)-(a/2-b)]
=cos(a-b/2)cos(a/2-b)+sin(a/2-b)sin(a-b/2)
cos(a-b/2)=-1/9,sin(a/2-b)=2/3
且π/2