Question

what will be the differentiation of 3cos2x ?​

Answer 1

Since 3 is constant with respect to x, the derivate of $\large\rm { 3 \cos 2x}$ with respect to x is $\large\rm { 3 \frac{d}{dx} [ \cos (2x)]}$

using chain rule,

$\large\rm { 3( - \sin (2x) \frac{d}{dx} [2x])}$

so, $\large\rm { -6 \sin (2x)}$ is the required answer.