若sinα+sin^2α=1,则cos^2α+cos^4α+cos^6α=?
问题描述:
若sinα+sin^2α=1,则cos^2α+cos^4α+cos^6α=?
答
用a代替
sina=1-sin²a=cos²a
所以原式=sina+sin²a+sin³a
=sina+sina(sina+sin²a)
=sina+sina
=2sina可标准答案是 -1±√5??是啊sina+sin²a=1且-1