sin(x+π/4)=-3/5
sinxcos(π/4)+cosxsin(π/4)=-3/5
√2/2(six+cosx)=-3/5
1/2(sinx+cosx)²=9/25
sin²x+2sinxcosx+cos²x=18/25
1+sin2x=18/25
sin2x=-7/25