1.

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

Answer»

Let us consider the LHS: secx – secx

(secx)2 – secx

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

(1 + tanx)2 – (1 + tanx)

1 + 2tanx + tanx – 1 – tanx

tanx + tanx

= RHS

∴ LHS = RHS

Thus proved.



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