sin(θ+π/4)=1/3
sinθcosπ/4+cosθsinπ/4=1/3
sinθ*√2/2+cosθ*√2/2=1/3
sinθ+cosθ=1/3*√2
(sinθ+cosθ)²=(1/3*√2)²
sin²θ+cos²θ+2sinθcosθ=2/9
1+sin2θ=2/9
sin2θ=2/9-1
sin2θ=-7/9