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Mathematics

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

1cos A1 + cos A=sin A1 + cos A\sqrt{\dfrac{1 - \text{cos A}}{\text{1 + cos A}}} = \dfrac{\text{sin A}}{\text{1 + cos A}}

Trigonometric Identities

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Answer

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

(1cos A)(1+cos A)(1 + cos A)(1 + cos A)(1cos2A)(1 + cos A)2sin2A(1 + cos A)2sin A1 + cos A.\Rightarrow \sqrt{\dfrac{(1 - \text{cos A})(1 + \text{cos A})}{\text{(1 + cos A)(1 + \text{cos A})}}} \\[1em] \Rightarrow \sqrt{\dfrac{(1 - \text{cos}^2 A)}{\text{(1 + cos A)}^2}} \\[1em] \Rightarrow \sqrt{\dfrac{\text{sin}^2 A}{\text{(1 + cos A)}^2}} \\[1em] \Rightarrow \dfrac{\text{sin A}}{\text{1 + cos A}}.

Since, L.H.S. = R.H.S. hence, proved that 1cos A1 + cos A=sin A1 + cos A\sqrt{\dfrac{1 - \text{cos A}}{\text{1 + cos A}}} = \dfrac{\text{sin A}}{\text{1 + cos A}}

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