(7x-20)(4x)=180

Solution for (7x-20)(4x)=180 equation:

(7x-20)(4x)=180

We move all terms to the left:

(7x-20)(4x)-(180)=0

We multiply parentheses

28x^2-80x-180=0

a = 28; b = -80; c = -180;
Δ = b2-4ac
Δ = -802-4·28·(-180)
Δ = 26560
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:

$\sqrt{\Delta}=\sqrt{26560}=\sqrt{64*415}=\sqrt{64}*\sqrt{415}=8\sqrt{415}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-80)-8\sqrt{415}}{2*28}=\frac{80-8\sqrt{415}}{56}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-80)+8\sqrt{415}}{2*28}=\frac{80+8\sqrt{415}}{56}
$