.5(2x-4)(x+5)=30

Solution for .5(2x-4)(x+5)=30 equation:

.5(2x-4)(x+5)=30

We move all terms to the left:

.5(2x-4)(x+5)-(30)=0

We multiply parentheses ..

.5(+2x^2+10x-4x-20)-30=0

We multiply parentheses

x^2+5x-2x-10-30=0

We add all the numbers together, and all the variables

x^2+3x-40=0

a = 1; b = 3; c = -40;
Δ = b2-4ac
Δ = 32-4·1·(-40)
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-13}{2*1}=\frac{-16}{2}
=-8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+13}{2*1}=\frac{10}{2}
=5
$