5x(2x-5)=20

Solution for 5x(2x-5)=20 equation:

5x(2x-5)=20

We move all terms to the left:

5x(2x-5)-(20)=0

We multiply parentheses

10x^2-25x-20=0

a = 10; b = -25; c = -20;
Δ = b2-4ac
Δ = -252-4·10·(-20)
Δ = 1425
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:

$\sqrt{\Delta}=\sqrt{1425}=\sqrt{25*57}=\sqrt{25}*\sqrt{57}=5\sqrt{57}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-5\sqrt{57}}{2*10}=\frac{25-5\sqrt{57}}{20}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+5\sqrt{57}}{2*10}=\frac{25+5\sqrt{57}}{20}
$