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Mathematics

Prove the following identities :

sec4 A (1 - sin4 A) - 2 tan2 A = 1

Trigonometric Identities

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Answer

Solving L.H.S. of the above equation :

⇒ sec4 A (1 - sin4 A) - 2 tan2 A

⇒ sec4 A (1 - sin2 A)(1 + sin2 A) - 2 tan2 A

By formula,

1 - sin2 A = cos2 A

⇒ sec4 A cos2 A (1 + sin2 A) - 2 tan2 A

⇒ sec4 A ×1sec2A\times \dfrac{1}{\text{sec}^2 A} (1 + sin2 A) - 2 tan2 A

⇒ sec2 A (1 + sin2 A) - 2 tan2 A

⇒ sec2 A + sec2 A sin2 A - 2 tan2 A

⇒ sec2 A + 1cos2A×\dfrac{1}{\text{cos}^2 A} \times sin2 A - 2 tan2 A

⇒ sec2 A + tan2 A - 2 tan2 A

⇒ sec2 A - tan2 A

⇒ 1.

Since, L.H.S. = R.H.S.

Hence, proved that sec4 A (1 - sin4 A) - 2 tan2 A = 1.

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