-3x^2-15+72=0

Solution for -3x^2-15+72=0 equation:

-3x^2-15+72=0

We add all the numbers together, and all the variables

-3x^2+57=0

a = -3; b = 0; c = +57;
Δ = b2-4ac
Δ = 02-4·(-3)·57
Δ = 684
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{684}=\sqrt{36*19}=\sqrt{36}*\sqrt{19}=6\sqrt{19}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{19}}{2*-3}=\frac{0-6\sqrt{19}}{-6}
=-\frac{6\sqrt{19}}{-6}
=-\frac{\sqrt{19}}{-1}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{19}}{2*-3}=\frac{0+6\sqrt{19}}{-6}
=\frac{6\sqrt{19}}{-6}
=\frac{\sqrt{19}}{-1}
$