-15x^2+50x+20=0

Solution for -15x^2+50x+20=0 equation:

-15x^2+50x+20=0

a = -15; b = 50; c = +20;
Δ = b2-4ac
Δ = 502-4·(-15)·20
Δ = 3700
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:

$\sqrt{\Delta}=\sqrt{3700}=\sqrt{100*37}=\sqrt{100}*\sqrt{37}=10\sqrt{37}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(50)-10\sqrt{37}}{2*-15}=\frac{-50-10\sqrt{37}}{-30}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(50)+10\sqrt{37}}{2*-15}=\frac{-50+10\sqrt{37}}{-30}
$