#### Answer

$x= ± \sqrt 11$

#### Work Step by Step

$5x^{2} = 55$
$x^{2} = \frac{55}{5}$ (Divide both sides by 5)
$x^{2} = 11$
$x = ±\sqrt 11$ (Use the square root property)
Check 1 :
Let $x = \sqrt 11$
$5x^{2} = 55$
$ 5(\sqrt 11)^{2}$ could be 55
$5 \times 11$ could be 55
$ 55 = 55$ Hence, true.
Check 2 :
Let $x = -\sqrt 11$
$5x^{2} = 55$
$ 5(-\sqrt 11)^{2}$ could be 55
$5 \times 11$ could be 55
$ 55 = 55$ Hence, true.
Therefore the solution set is ($\sqrt 11, -\sqrt 11$)