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Mathematics

Prove the following identities, where the angles involved are acute angles for which the trigonometric ratios are defined:

2 sec2 θ - sec4 θ - 2 cosec2 θ + cosec4 θ = cot4 θ - tan4 θ.

Trigonometric Identities

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Answer

The L.H.S of the equation can be written as,

⇒ 2(1 + tan2 θ) - (sec2 θ)2 - 2(1 + cot2 θ) + (cosec2 θ)2
⇒ 2 + 2tan2 θ - (1 + tan2 θ)2 - 2 - 2cot2 θ + (1 + cot2 θ)2
⇒ 2 + 2tan2 θ - (1 + tan4 θ + 2tan2 θ) - 2 - 2cot2 θ + (1 + cot4 θ + 2cot2 θ)
⇒ 2 + 2tan2 θ - 1 - tan4 θ - 2tan2 θ - 2 - 2cot2 θ + 1 + cot4 θ + 2cot2 θ
⇒ 2 - 2 + 2tan2 θ - 2tan2 θ + 2cot2 θ - 2cot2 θ + 1 - 1 + cot4 θ - tan4 θ
⇒ cot4 θ - tan4 θ.

Since, L.H.S. = R.H.S. hence, proved that 2 sec2 θ - sec4 θ - 2 cosec2 θ + cosec4 θ = cot4 θ - tan4 θ.

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