[(sina+cosa)^2-(sina-cosa)^2]/[tana-sina*cosa]

1。将（sinα+cosα)^2和（sinα-cosα)^2拆开后化简2。tanα写成sinα/cosα,在与sinαcosα通分3。化简用到的公式：(a+b)^2=a^2+b^2+2absin^2α+cos^2α=1sinα/cosα=tanαcosα/sinα=cotα原式=[sin^2a+cos^2a+2sinacosa-sin^2a-cos^2a+2sinacosa]/tana-sinacosa]=4sinacosa/[(sina/cosa)-sinacosa]=4sinacosa/sina(1-cos^2 a)/cosa=4sinacos^2a/sina*sin^2 a=4sinacos^2a/sin^3 a=4cos^2a