Đáp án:
Giải thích các bước giải:
`cos^2 \alpha+cos^2 \alpha. sin^2 \alpha+sin^4 \alpha`
`= sin^4 \alpha+sin^2 \alpha. cos^2 \alpha+cos^2 \alpha`
`=sin^4 \alpha+2sin^2 \alpha. cos^2 \alpha+cos^4 \alpha-cos^4 \alpha-sin^2 \alpha. cos^2 \alpha+cos^2 \alpha`
`=(sin^2 \alpha+cos^2 \alpha)^2-cos^4 \alpha+cos^2 \alpha(1-sin^2 \alpha)`
`=1-cos^4 \alpha+cos^2 \alpha. cos^2 \alpha`
`=1-cos^4 \alpha+cos^4 \alpha`
`=1`
