Question

The answer is 1.5.Its differentiation

Answer 1

$\frac{d}{dx} f(x) = 9 \cos(x) + 3 \cos(3x) \\ \frac{d}{dx} f( \frac{\pi}{3} ) = 9 \cos( \frac{\pi}{3} ) + 3 \cos( \frac{3\pi}{3} ) \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 9 \times \frac{1}{2} + 3 \times - 1 = 4.5 - 3 = 1.5$

Answer 2

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