(x+2)(2x-5)-56=0

Solution for (x+2)(2x-5)-56=0 equation:

(x+2)(2x-5)-56=0

We multiply parentheses ..

(+2x^2-5x+4x-10)-56=0

We get rid of parentheses

2x^2-5x+4x-10-56=0

We add all the numbers together, and all the variables

2x^2-1x-66=0

a = 2; b = -1; c = -66;
Δ = b2-4ac
Δ = -12-4·2·(-66)
Δ = 529
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{529}=23$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-23}{2*2}=\frac{-22}{4}
=-5+1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+23}{2*2}=\frac{24}{4}
=6
$