1.

Prove the identity: sec4 x – sec2 x = tan4 x + tan2 x

Answer»

Let us consider the LHS: sec4 x – sec2 x

(sec2 x)2 – sec2 x

On using the formula, sec2 θ = 1 + tan2 θ.

(1 + tan2 x)2 – (1 + tan2 x)

1 + 2tan2 x + tan4 x – 1 – tan2 x

tan4 x + tan2 x

= RHS

∴ LHS = RHS

Thus proved.



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