4x(5x-7)=20

Solution for 4x(5x-7)=20 equation:

4x(5x-7)=20

We move all terms to the left:

4x(5x-7)-(20)=0

We multiply parentheses

20x^2-28x-20=0

a = 20; b = -28; c = -20;
Δ = b2-4ac
Δ = -282-4·20·(-20)
Δ = 2384
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:

$\sqrt{\Delta}=\sqrt{2384}=\sqrt{16*149}=\sqrt{16}*\sqrt{149}=4\sqrt{149}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-4\sqrt{149}}{2*20}=\frac{28-4\sqrt{149}}{40}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+4\sqrt{149}}{2*20}=\frac{28+4\sqrt{149}}{40}
$