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Mathematics

x = (cosec A + cot A)(1 - cos A)

Assertion (A): x = sin A

Reason (R): x = (1sin A+cos Asin A)(1cos A)=sin2Asin A=sin A\Big(\dfrac{1}{\text{sin A}} + \dfrac{\text{cos A}}{\text{sin A}}\Big)(1 - \text{cos A}) = \dfrac{\text{sin}^2 A}{\text{sin A}} = \text{sin A}

  1. A is true, R is false.

  2. A is false, R is true.

  3. Both A and R are true and R is correct reason for A.

  4. Both A and R are true and R is incorrect reason for A.

Trigonometric Identities

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Answer

Given, x = (cosec A + cot A)(1 - cos A)

x=(1sin A+cos Asin A)(1cos A)=(1+cos Asin A)(1cos A)=(1+cos A)(1cos A)sin A=(1cos2Asin A)=(sin2Asin A)=sin A.\Rightarrow x = \Big(\dfrac{1}{\text{sin A}} + \dfrac{\text{cos A}}{\text{sin A}}\Big)(1 - \text{cos A})\\[1em] = \Big(\dfrac{1 + \text{cos A}}{\text{sin A}}\Big)(1 - \text{cos A})\\[1em] = \dfrac{(1 + \text{cos A})(1 - \text{cos A})}{\text{sin A}}\\[1em] = \Big(\dfrac{1 - \text{cos}^2 A}{\text{sin A}}\Big)\\[1em] = \Big(\dfrac{\text{sin}^2 A}{\text{sin A}}\Big)\\[1em] = \text{sin A}.

∴ Both A and R are true and R is correct reason for A.

Hence, option 3 is the correct option.

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