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  1. If tan4θ + tan2θ = 1 then the value of cos4θ + cos2θ is
    1. 2
    2. 0
    3. 1
    4. –1
Correct Option: C

tan4θ + tan2θ = 1
⇒  tan2θ (tan2θ + 1) = 1
⇒  tan2θ . sec2θ = 1

⇒  tan2θ =
1
 = cos2θ.
sec2θ

∴  cos4θ + cos2θ = tan4θ + tan2θ = 1


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