根据cos（a+b)=cos(a)cos(b)-sin(a)sin(b) cos（a-b)=cos(a)cos(b)+sin(a)sin(b) xiangjia cos(a+b)+cos(a-b)=2cos(a)cos(b) 设 a+b=A a-b=B 得 a=(A+B)/2 b==(A-B)/2 suoyi cos(A)+cos(B)=cos(a+b)+cos(a-b)=2cos(a)cos(b)=2cos(A+B/2 )cos(A-B/2) A1cos(A)+A2cos(B)=A1[cosA)+A2/A1cos(B)]
答：上面的符号你是怎么打上去的？详情>>
答：详情>>
