5x^2-12x-81=0

Solution for 5x^2-12x-81=0 equation:

5x^2-12x-81=0

a = 5; b = -12; c = -81;
Δ = b2-4ac
Δ = -122-4·5·(-81)
Δ = 1764
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1764}=42$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-42}{2*5}=\frac{-30}{10}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+42}{2*5}=\frac{54}{10}
=5+2/5
$