How do I prove that ( (1-cos A) / (1+cos A) ) = (tan (A/2))^2 ? I have tried using the half angle formulae for cos A but have not entirely finished the question.
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Originally Posted by Stuck Man How do I prove that ( (1-cos A) / (1+cos A) ) = (tan (A/2))^2 ? I have tried using the half angle formulae for cos A but have not entirely finished the question. $\displaystyle \displaystyle \tan^2\left(\frac{A}{2}\right) = \frac{\sin^2\left(\frac{A}{2}\right)}{\cos^2\left( \frac{A}{2}\right)} = \frac{\frac{1-\cos{A}}{2}}{\frac{1+\cos{A}}{2}} = \frac{1-\cos{A}}{1+\cos{A}}$
Thats much shorter than I expected. I used the 'little t' formula for cos A. Thanks.
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