Question

求解！急急急！

Answer 1

π/2<A<3π/4
π/2<B<3π/4
所以π<A+B<3π/2
所以cos(A+B)<0
sin(A+B)=-3/5
所以cos(A+B)=-4/5

-3π/4<-B<-π/2
π/2<A<3π/4
所以-π/4<A-B<π/4
A>B,
所以0<A-B<π/4
sin(A-B)>0
cos(A-B)=12/13
所以sin(A-B)=5/13

sin2A=sin[(A+B)+(A-B)]
=sin(A+B)cos(A-B)+cos(A+B)sin(A-B)
=-56/65

追问

谢谢你哈