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Mathematics

Prove the following identities :

1sin2A1 + cos A=cos A1 - \dfrac{\text{sin}^2 A}{\text{1 + cos A}} = \text{cos A}

Trigonometric Identities

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Answer

By formula,

sin2 A = 1 - cos2 A

Solving L.H.S. of the equation :

11cos2A1 + cos A1(1 - cos A)(1 + cos A)1 + cos A1(1 - cos A)11+cos Acos A.\Rightarrow 1 - \dfrac{1 - \text{cos}^2 A}{\text{1 + cos A}} \\[1em] \Rightarrow 1 - \dfrac{\text{(1 - cos A)(1 + cos A)}}{\text{1 + cos A}} \\[1em] \Rightarrow 1 - (\text{1 - cos A}) \\[1em] \Rightarrow 1 - 1 + \text{cos A} \\[1em] \Rightarrow \text{cos A}.

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

Hence, proved that 1sin2A1 + cos A=cos A1 - \dfrac{\text{sin}^2 A}{\text{1 + cos A}} = \text{cos A}.

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