哈哈!sin2a=2sina*cosa = 2或者－2.sin2a的值怎么可能超过正负1!1/cosa-1/sina=1 (sina-cosa)/cosa*sina=1 sinacosa=sina-cosa -----------(1)另外sina^2 + cosa^2 = 1 ------(2) 由(2)-2*(1)得sina^2+cosa^2-2ainac...