∫sinxsin(x+ω τ)dx
=-(1/2)∫cos(ω τ)dx+(1/2)∫cos(2x+ω τ)dx
∫[0,2π] sinxsin(x+ω τ)dx
= -cos(ω τ)π + (1/4) [sin(ω τ)-sin(ω τ)]
=-cos(ω τ)π
∫[0,2π]sinxsin(x+ω τ)dx
=-1/2∫[0,2π][cos(2x+ω τ)-cos(ω τ)]dx
=-1/2*[1/2sin(2x+ω τ)-cos(ω τ)x][0,2π]
=πcos(ω τ)
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