MHB How can you factor out x from the original term?

AI Thread Summary
To factor out x from the term $\sqrt{2x^2 + 1}$, it can be rewritten as $x\sqrt{2 + \frac{1}{x^2}}$ for positive x. The equality holds because $2x^2 + 1$ can be expressed as $x^2(2 + \frac{1}{x^2})$. The identity $\sqrt{x^2} = x$ is applicable when x is greater than zero. For non-zero x, the expression can be generalized to $\sqrt{2x^2 + 1} = |x|\sqrt{2 + \frac{1}{x^2}}$. Understanding these steps clarifies how to factor out x correctly.
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In a text,

We have this:

$\sqrt{2x^2 + 1}$

is equal to

$x \sqrt{2 + \frac{1}{x}}$

I am confused as to how to factor out x from the original term.
 
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The two expressions are not equal. Actually,

$$\sqrt{2x^2 + 1} = x\sqrt{2 + \frac{1}{x^2}}\quad \text{for}\quad x > 0.$$

For if $x > 0$,

$$2x^2 + 1 = 2x^2 + \frac{x^2}{x^2} = x^2\Bigl(2 + \frac{1}{x^2}\Bigr),$$

so that

$$\sqrt{2x^2 + 1} = \sqrt{x^2\Bigl(2 + \frac{1}{x^2}\Bigr)} = \sqrt{x^2} \sqrt{2 + \frac{1}{x^2}} = x\sqrt{2 + \frac{1}{x^2}}.$$

Note the use of the identity $\sqrt{x^2} = x$, $x > 0$.

More generally,

$$\sqrt{2x^2 + 1} = |x|\sqrt{2 + \frac{1}{x^2}}\quad \text{for} \quad x \neq 0$$
 
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