因为 sin(a+b)=-3/5 cos(a+b)=4/5sin(b-π/4)=12/13 cos（b-π/4）=5/13cos(a+π/4)=cos(a+b-b+π/4）= cos(a+b)cos(b-π/4）+sin(a+b)sin(b-π/4)=20/65-36/65=-16/65a和b属于四分之三派 这个应该是个区间你没打出...