(x-1)(5x-20)=0

Solution for (x-1)(5x-20)=0 equation:

(x-1)(5x-20)=0

We multiply parentheses ..

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

We get rid of parentheses

5x^2-20x-5x+20=0

We add all the numbers together, and all the variables

5x^2-25x+20=0

a = 5; b = -25; c = +20;
Δ = b2-4ac
Δ = -252-4·5·20
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-15}{2*5}=\frac{10}{10}
=1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+15}{2*5}=\frac{40}{10}
=4
$