Question

Derivative of the function $f\left(x\right)=7x^{-3}$ is

• A. $21x^{-4}$
• B. $-21x^{-4}$
• C. $21x^4$
• D. $-21x^4$

Answer 1

The correct option is B $-21x^{-4}$

Applying
$\frac{d}{dx}\left(x^n\right)=n{x}^{n-1}$,
we get
$\frac{d}{dx}\left(7x^{-3}\right)=7\frac{d}{dx}{x}^{-3}$
$=7(-3)x^{{}^{-3-1}}=-21x^{-4}$