cos(a-b)=-(4/5)cos(a+b)=12/13a-b=(π/2、π) (a+b)=(3π/2 2π) 求:cos2a cos2b

问题描述:

cos(a-b)=-(4/5)cos(a+b)=12/13a-b=(π/2、π) (a+b)=(3π/2 2π) 求:cos2a cos2b

cos(a-b)=-4/5
cos(a+b)=12/13
π/2