# Express the Following as the Sum Or Difference of Sines and Cosines:2 Sin 4x Sin 3x - Mathematics

Sum

Express the following as the sum or difference of sines and cosines:
2 sin 4x sin 3x

#### Solution

$2\left( \sin 4x \right) \left( \sin 3x \right)$
$= \cos \left( 4x - 3x \right) - \cos \left( 4x + 3x \right) \left[ \because 2 \sin A \sin B = \cos(A - B) - \cos(A + B) \right]$
$= \cos x - \cos 7x$

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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 8 Transformation formulae
Exercise 8.1 | Q 1.3 | Page 6