因为sin(x-π/4)=3/5
所以cos(x-π/4)=4/5或-4/5
sin(2x-π/2)=2sin(x-π/4)cos(x-π/4)=24/25或-24/25
cos(2x)=-24/25或24/25
sin(2x)=7/25或-7/25
又因为sin(x-π/4)>0
所以sin(2x)>0
sin(2x)=7/25
因为sin(x-π/4)=3/5
所以cos(x-π/4)=4/5或-4/5
sin(2x-π/2)=2sin(x-π/4)cos(x-π/4)=24/25或-24/25
cos(2x)=-24/25或24/25
sin(2x)=7/25或-7/25
又因为sin(x-π/4)>0
所以sin(2x)>0
sin(2x)=7/25