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Prove that:$ \frac{\tan A+\tan B}{\cot A+\cot B}=\tan A \tan B $
To do:
We have to prove that \( \frac{\tan A+\tan B}{\cot A+\cot B}=\tan A \tan B \).
Solution:
We know that,
$\sin^2 A+\cos^2 A=1$
$\operatorname{cosec}^2 A-\cot^2 A=1$
$\sec^2 A-\tan^2 A=1$
$\cot A=\frac{\cos A}{\sin A}$
$\tan A=\frac{\sin A}{\cos A}$
$\operatorname{cosec} A=\frac{1}{\sin A}$
$\sec A=\frac{1}{\cos A}$
Therefore,
$\frac{\tan A+\tan B}{\cot A+\cot B}=\frac{\frac{\sin A}{\cos A}+\frac{\sin B}{\cos B}}{\frac{\cos A}{\sin A}+\frac{\cos B}{\sin B}}$
$=\frac{\frac{\sin A \cos B+\cos A \sin B}{\cos A \cos B}}{\frac{\sin A \cos B+\cos A \sin B}{\sin A \sin B}}$
$=\frac{\sin A \sin B}{\cos A \cos B}$
$=\frac{\sin A}{\cos A}\times\frac{\sin B}{\cos B}$
$=\tan A \tan B$
Hence proved.
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