9x^2-72x-36=0

Solution for 9x^2-72x-36=0 equation:

9x^2-72x-36=0

a = 9; b = -72; c = -36;
Δ = b2-4ac
Δ = -722-4·9·(-36)
Δ = 6480
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:

$\sqrt{\Delta}=\sqrt{6480}=\sqrt{1296*5}=\sqrt{1296}*\sqrt{5}=36\sqrt{5}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-72)-36\sqrt{5}}{2*9}=\frac{72-36\sqrt{5}}{18}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-72)+36\sqrt{5}}{2*9}=\frac{72+36\sqrt{5}}{18}
$