5x^2-20x-11=10

Solution for 5x^2-20x-11=10 equation:

5x^2-20x-11=10

We move all terms to the left:

5x^2-20x-11-(10)=0

We add all the numbers together, and all the variables

5x^2-20x-21=0

a = 5; b = -20; c = -21;
Δ = b2-4ac
Δ = -202-4·5·(-21)
Δ = 820
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:

$\sqrt{\Delta}=\sqrt{820}=\sqrt{4*205}=\sqrt{4}*\sqrt{205}=2\sqrt{205}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-2\sqrt{205}}{2*5}=\frac{20-2\sqrt{205}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+2\sqrt{205}}{2*5}=\frac{20+2\sqrt{205}}{10}
$