(1-sin^6θ-cos^6θ)/(1-sin^4θ-cos^4θ)

来源:学生作业帮助网 编辑:作业帮 时间:2024/11/17 05:39:24

(1-sin^6θ-cos^6θ)/(1-sin^4θ-cos^4θ)
(1-sin^6θ-cos^6θ)/(1-sin^4θ-cos^4θ)

(1-sin^6θ-cos^6θ)/(1-sin^4θ-cos^4θ)
1-sin^6θ-cos^6θ
=1-[(sin^2θ)^3+(cos^2θ)^3]
=1-(sin^2θ+cos^2θ)(sin^4θ-sin^2θcos^2θ+cos^4θ)
=1-(sin^4θ-sin^2θcos^2θ+cos^4θ)
=1-(sin^4θ+2sin^2θcos^2θ+cos^4θ-3sin^2θcos^2θ)
=1-[(sin^2θ+cos^2θ)^2-3sin^2θcos^2θ]
=3sin^2θcos^2θ
1-sin^4θ-cos^4θ
=1-(sin^4θ+cos^4θ)
=1-[(sin^4θ+2sin^2θcos^2θ+cos^4θ-2sin^2θcos^2θ)]
=1-[(sin^2θ+cos^2θ)^2-2sin^2θcos^2θ]
=2sin^2θcos^2θ
所以:(1-sin^6θ-cos^6θ)/(1-sin^4θ-cos^4θ)
=(3sin^2θcos^2θ)/(2sin^2θcos^2θ)
=3/2.