sin(x-3派/4)cos(x-π/4)=-1/4,求cos4x

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sin(x-3派/4)cos(x-π/4)=-1/4,求cos4x
sin(x-3派/4)cos(x-π/4)=-1/4,求cos4x

sin(x-3派/4)cos(x-π/4)=-1/4,求cos4x

-1/2