-5x^2-20x+7=0

Solution for -5x^2-20x+7=0 equation:

-5x^2-20x+7=0

a = -5; b = -20; c = +7;
Δ = b2-4ac
Δ = -202-4·(-5)·7
Δ = 540
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:

$\sqrt{\Delta}=\sqrt{540}=\sqrt{36*15}=\sqrt{36}*\sqrt{15}=6\sqrt{15}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-6\sqrt{15}}{2*-5}=\frac{20-6\sqrt{15}}{-10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+6\sqrt{15}}{2*-5}=\frac{20+6\sqrt{15}}{-10}
$