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Mathematics

Prove the following identity:

(sin A + cosec A)2 + (cos A + sec A)2 = 7 + tan2 A + cot2 A

Trigonometric Identities

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Answer

By formula,

sin2 A + cos2 A = 1

sec2 A = 1 + tan2 A

cosec2 A = 1 + cot2 A

Solving L.H.S. of the equation :

⇒ (sin A + cosec A)2 + (cos A + sec A)2 = 7 + tan2 A + cot2 A

⇒ sin2 A + cosec2 A + 2 sin A. cosec A + cos2 A + sec2 A + 2 cos A. sec A

⇒ sin2 A + 1 + cot2 A + 2 × sin A × 1sinA\dfrac{1}{\sin A} + cos2 A + 1 + tan2 A + 2 × cos A × 1cosA\dfrac{1}{\cos A}

⇒ sin2 A + cos2 A + 1 + cot2 A + 2 + 1 + tan2 A + 2

⇒ 1 + 1 + 2 + 1 + 2 + cot2 A + tan2 A

⇒ 7 + tan2 A + cot2 A.

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

Hence, proved that (sin A + cosec A)2 + (cos A + sec A)2 = 7 + tan2 A + cot2 A.

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