9x2-8x-72=0

Solution for 9x2-8x-72=0 equation:

9x^2-8x-72=0

a = 9; b = -8; c = -72;
Δ = b2-4ac
Δ = -82-4·9·(-72)
Δ = 2656
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:

$\sqrt{\Delta}=\sqrt{2656}=\sqrt{16*166}=\sqrt{16}*\sqrt{166}=4\sqrt{166}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-4\sqrt{166}}{2*9}=\frac{8-4\sqrt{166}}{18}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+4\sqrt{166}}{2*9}=\frac{8+4\sqrt{166}}{18}
$