f(x)=sin(wx+π/4)(x屬于R,w大于0)的最小正周期為πT=2π/w=π,w=2y=f(x)的圖像向左平移|α|,所得圖像關(guān)于y軸對稱,y=f(x+|α|)=sin(2(x+|α|)+π/4)=sin(2x+2|α|+π/4)=±cos2x2|α|+π/4=kπ+π/22|α|=kπ+π/4|...y=f(x+|α|)=sin(2(x+|α|)+π/4)=sin(2x+2|α|+π/4)=±cos2x中的sin(2x+2|α|+π/4)=±cos2x這一步不懂！求解？y=f(x)的圖像向左平移|α|,所得圖像關(guān)于y軸對稱即：y=f(x+|α|)=sin(2x+2|α|+π/4)圖像關(guān)于y軸對稱說明y=f(x+|α|)=sin(2x+2|α|+π/4)是偶函數(shù)，y=cos2x或者y=-cos2x是偶函數(shù)所以sin(2x+2|α|+π/4)=±cos2x這樣就有2|α|+π/4=kπ+π/2因為sin(2x±π/2）=±cos2x