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Mathematics

Prove the following identities :

1 + sin Acosec A - cot A1 - sin Acosec A + cot A\dfrac{\text{1 + sin A}}{\text{cosec A - cot A}} - \dfrac{\text{1 - sin A}}{\text{cosec A + cot A}} = 2(1 + cot A)

Trigonometric Identities

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Answer

Solving L.H.S. of the equation :

1 + sin Acosec A - cot A1 - sin Acosec A + cot A(1 + sin A)(cosec A + cot A)(1 - sin A)(cosec A - cot A)cosec2Acot2A\Rightarrow \dfrac{\text{1 + sin A}}{\text{cosec A - cot A}} - \dfrac{\text{1 - sin A}}{\text{cosec A + cot A}} \\[1em] \Rightarrow \dfrac{\text{(1 + sin A)(cosec A + cot A)} - \text{(1 - sin A)(cosec A - cot A)}}{\text{cosec}^2 A - \text{cot}^2 A}

By formula,

cosec2 A - cot2 A = 1

⇒ (1 + sin A)(cosec A + cot A) - (1 - sin A)(cosec A - cot A)

⇒ cosec A + cot A + sin A cosec A + sin A cot A - (cosec A - cot A - sin A cosec A + sin A cot A)

⇒ cosec A - cosec A + cot A + cot A + sin A cosec A + sin A cosec A + sin A cot A - sin A cot A

⇒ 2 cot A + 2 sin A cosec A

⇒ 2 cot A + 2 sin A×1sin A2 \text{ sin A} \times \dfrac{1}{\text{sin A}}

⇒ 2 cot A + 2

⇒ 2(cot A + 1).

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

Hence, proved that 1 + sin Acosec A - cot A1 - sin Acosec A + cot A\dfrac{\text{1 + sin A}}{\text{cosec A - cot A}} - \dfrac{\text{1 - sin A}}{\text{cosec A + cot A}} = 2(1 + cot A).

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