(cosα)^4+(sinαcosα)^2+(sinα)^2
=(cosα)^2.((cosα)^2+(sinα)^2)+(sinα)^2
=(cosα)^2+(sinα)^2
=1不明白第二步是怎么来的。。。(cosα)^4+(sinαcosα)^2+(sinα)^2=[(cosα)^4+(sinαcosα)^2]+(sinα)^2==(cosα)^2.[ (cosα)^2+(sinα)^2]+(sinα)^2