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

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Answer 1 · 2016-07-12T22:30:45

$x = +3sqrt2" or " x = -3sqrt2$

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.

$5x^2 = 90 " "÷ 5$

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

$x = +-sqrt18$

$x = +3sqrt2" or " x = -3sqrt2$

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

How do you solve 5x^2 - 90 = 05x^2 - 90 = 0?