Question

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Answer 1

tan4a+tan2a=1

⇒(tan2a+1)tan2a=1

⇒sec2atan2a=1

⇒(1cos2a)tan2a=1

⇒tan2a=cos2a

⇒sin2acos2a=cos2a

⇒sin2a=cos4a

⇒1−cos2a=cos4a

⇒cos4a+cos2a=1