若cos(θ-pai/4)=a,求sin(θ+pai/4)

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若cos(θ-pai/4)=a,求sin(θ+pai/4)

cos(θ-pai/4)
=sin(pai/2-θ-pai/4)
=sin(pai/4-θ)=a
sin(θ+pai/4)
=-sin(pai/4-θ)
=-a

a+π/4 =π/2+a-π/4
sin(a+π/4)
=sin(π/2+a-π/4)
= -cos(a-π/4)
=-a