20x(4x-15)=0

Solution for 20x(4x-15)=0 equation:

20x(4x-15)=0

We multiply parentheses

80x^2-300x=0

a = 80; b = -300; c = 0;
Δ = b2-4ac
Δ = -3002-4·80·0
Δ = 90000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{90000}=300$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-300)-300}{2*80}=\frac{0}{160}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-300)+300}{2*80}=\frac{600}{160}
=3+3/4
$