Question

- 81 = 0" align="absmiddle" class="latex-formula">

Answer 1

Sum 81 to both sides to get

$4x^2 = 81$

Divide both sides by 4 to get

$x^2 = \frac{81}{4} = \frac{9^2}{2^2}$

Consider the square root of both sides. Note that this requires the $\pm$ sign, since $a^2=b^2$ implies $a=b$, but also $a=-b$. So, the solutions are

$x = \pm\sqrt{\frac{9^2}{2^2}} = \pm\frac{9}{2}$