# If a + B = C, Then Write the Value of Tan a Tan B Tan C. - Mathematics

Short Note

If A + B = C, then write the value of tan A tan B tan C.

#### Solution

$\tan A \tan B \tan C = \tan A \tan B \tan(A + B) \left[ \text{ Using } A + B = C \right]$
$= \tan A \tan B \times \frac{\tan A + \tan B}{1 - \tan A \tan B}$
$= \frac{\tan^2 A\tan B + \tan A \tan^2 B}{1 - \tan A \tan B}$
$= \frac{\tan^2 A\tan B + \tan A \tan^2 B + \tan A + \tan B - \tan A - \tan B}{1 - \tan A \tan B}$
$= \frac{- \tan A(1 - \tan A\tan B) - \tan B(1 - \tan A\tan B) + \tan A + \tan B}{1 - \tan A \tan B}$
$= \frac{- (1 - \tan A\tan B)\left( \tan A + \tan B \right) + \tan A + \tan B}{1 - \tan A \tan B}$
$= \frac{\tan A + \tan B}{1 - \tan A \tan B} - \tan A - \tan B$
$= \tan(A + B) - \tan A - \tan B$
$= \tan C - \tan A - \tan B$


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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 7 Values of Trigonometric function at sum or difference of angles
Q 10 | Page 27