# How do you solve 5x^2 - 90 = 0?

Jul 12, 2016

$x = + 3 \sqrt{2} \text{ or } x = - 3 \sqrt{2}$

#### Explanation:

Usually to solve a quadratic equation, we make it equal to 0.
However in this case, as there is no term in x, we can use a different method.

5x^2 = 90 " "÷ 5

x^2 = 18 " find the" +- sqrt

$x = \pm \sqrt{18}$

$x = + 3 \sqrt{2} \text{ or } x = - 3 \sqrt{2}$

If the constant had been a perfect square we could have factorised as difference of two squares, but 18 is not a square.