已知sin(派/4)+x=-1/5,求cos(3/4派)+x的值

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已知sin(派/4)+x=-1/5,求cos(3/4派)+x的值

cos[(3/4派)+x]
=cos[π-(π/4-x)]
=-cos(π/4-x)
=-cos[(π/2-(π/4+x)]
=-sin(π/4+x)
=1/5