15x^2-15x-72=0

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

15x^2-15x-72=0

a = 15; b = -15; c = -72;
Δ = b2-4ac
Δ = -152-4·15·(-72)
Δ = 4545
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:

$\sqrt{\Delta}=\sqrt{4545}=\sqrt{9*505}=\sqrt{9}*\sqrt{505}=3\sqrt{505}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-3\sqrt{505}}{2*15}=\frac{15-3\sqrt{505}}{30}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+3\sqrt{505}}{2*15}=\frac{15+3\sqrt{505}}{30}
$