Let $f: \mathbb{R}-\{2,6\} \rightarrow \mathbb{R}$ be real valued function defined as $f(x)=\frac{x^2+2 x+1}{x^2-8 x+12}$. Then range of $f$ is

Question

Let $f: \mathbb{R}-\{2,6\} \rightarrow \mathbb{R}$ be real valued function

defined as $f(x)=\frac{x^2+2 x+1}{x^2-8 x+12}$.

Then range of $f$ is

$ \left(-\infty,-\frac{21}{4}\right] \cup[1, \infty) $

$\left(-\infty,-\frac{21}{4}\right) \cup(0, \infty) $

$\left(-\infty,-\frac{21}{4}\right] \cup[0, \infty) $

$\left(-\infty,-\frac{21}{4}\right] \cup\left[\frac{21}{4}, \infty\right)$

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