Question

Let $f(x)=x-\frac{1}{x}$ then $f^{\prime }(-1)$ is

• A. 0
• B. 2
• C. 1
• D. -2

Answer 1

Answer: (B)

Given $f(x)=x-\frac{1}{x}$
$\Rightarrow f^{\prime }(x)=1-\left(-\frac{1}{x^2}\right)=1+\frac{1}{x^2}$
$\Rightarrow f^{\prime }(-1)=1+\frac{1}{(-1{)}^2}=2$