Answer
$x=-\dfrac{4\sqrt{15}}{3}, \dfrac{4\sqrt{15}}{3}$
Work Step by Step
Divide both sides by $3$:
$\dfrac{3x^{2}}{3}=\dfrac{80}{3}$
$x^2=\dfrac{16(5)}{3}$
Take the square root of both sides:
$x=\pm\sqrt{\dfrac{16(5)}{3}}$
Rationalize the denominator by multiplying $3$ to both the numerator and the denominator of the radicand:
$x=\pm4\sqrt{\dfrac{16(5)(3)}{3(3)}}$
Take out the square roots of $16$ and $3(3)$, which are $4$ and $3$, respectively:
$x=\pm\dfrac{4\sqrt{5(3)}}{3}$
$x=\pm\dfrac{4\sqrt{15}}{3}$
