x^2-28x-39=0

Solution for x^2-28x-39=0 equation:

x^2-28x-39=0

a = 1; b = -28; c = -39;
Δ = b2-4ac
Δ = -282-4·1·(-39)
Δ = 940
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:

$\sqrt{\Delta}=\sqrt{940}=\sqrt{4*235}=\sqrt{4}*\sqrt{235}=2\sqrt{235}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-2\sqrt{235}}{2*1}=\frac{28-2\sqrt{235}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+2\sqrt{235}}{2*1}=\frac{28+2\sqrt{235}}{2}
$