化简cot^2 A(tan^2 A-sin^2 A)

化简cot^2 A(tan^2 A-sin^2 A)
化简cot^2 A(tan^2 A-sin^2 A)

化简cot^2 A(tan^2 A-sin^2 A)
tanA*cosA=1
cotA=cosA/sinA
所以cot^2 A(tan^2 A-sin^2 A)
=cot^2 A*tan^2 A-cot^2 Asin^2 A
=1-cos^2 A
=sin^2 A

cot^2A(tan^2A-sin^2A)
=1-cos^2Asin^2A/sin^2A
=1-cos^2A
=sin^2A

(cos^2a/sin^2a)*[(sin^2a/cos^2a)-sin^2a]=cos^2a