Question 272153
I assume the problem is to solve:
{{{3x^4 +15x^2 -72 = 0}}}
.
Factoring, we arrive at: 
{{{(3x^2 - 24)(x^2 + 3) = 0}}}
.
Real solutions will be found where
{{{(3x^2 -24) = 0}}}
or
{{{(x^2 +3 ) = 0}}}
.
{{{3x^2 - 24 = 0}}}
{{{3x^2 = 24}}}
{{{x^2 = 8}}}
{{{x = sqrt(8) = 2*sqrt(2)}}}
or
{{{x = -sqrt(8) = -2*sqrt(2)}}}

.
{{{x^2 + 3 = 0}}}
{{{x^2 = -3}}}
There are no real solutions for this part.