#### Answer

$$(2x - 7)(2x + 7)$$

#### Work Step by Step

On observation, we can see that this expression is the difference of two squares. The form for expressions written as the difference of two cubes is:
$$(A - B)(A + B)$$
where $A$ is the square root of the leading term and $B$ is the square root of the last term.
In this problem, we have $A$ as $\sqrt (4x^2)$ or $2x$ and $B$ as $\sqrt 49$ or $7$. We plug these values into the formula:
$$(2x - 7)(2x + 7)$$