如图单位长度为半径的圆,假定OA与x轴正半轴的夹角是2x,则2x-π/2就是与之垂直的OA'与x轴正半轴的夹角(顺时针旋转90度).sin2x是A的纵坐标,cos2x是A的横坐标sin(2x-π/2) 是A'的纵坐标,数值上等...
sin(2x-π/2)=-cos2x是怎么来的,
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