(2x-4)*(2x+5)=0

Solution for (2x-4)*(2x+5)=0 equation:

(2x-4)(2x+5)=0

We multiply parentheses ..

(+4x^2+10x-8x-20)=0

We get rid of parentheses

4x^2+10x-8x-20=0

We add all the numbers together, and all the variables

4x^2+2x-20=0

a = 4; b = 2; c = -20;
Δ = b2-4ac
Δ = 22-4·4·(-20)
Δ = 324
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{324}=18$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-18}{2*4}=\frac{-20}{8}
=-2+1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+18}{2*4}=\frac{16}{8}
=2
$