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If $y=\dfrac{1}{x^n}$, then $\dfrac{dy}{dx}$ is
A$\dfrac{n}{x^{n+1}}$
B$-\dfrac{n}{x^{n+1}}$
C$-\dfrac{1}{x^{n-1}}$
D$\dfrac{1}{x^{n+1}}$
Answer & Solution
Correct answer: B. $-\dfrac{n}{x^{n+1}}$
Write $y=x^{-n}$. Then by the power rule, $\dfrac{dy}{dx}=-n x^{-n-1}=-\dfrac{n}{x^{n+1}}$.
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