(5x+5)(4x-2)=75

Solution for (5x+5)(4x-2)=75 equation:

(5x+5)(4x-2)=75

We move all terms to the left:

(5x+5)(4x-2)-(75)=0

We multiply parentheses ..

(+20x^2-10x+20x-10)-75=0

We get rid of parentheses

20x^2-10x+20x-10-75=0

We add all the numbers together, and all the variables

20x^2+10x-85=0

a = 20; b = 10; c = -85;
Δ = b2-4ac
Δ = 102-4·20·(-85)
Δ = 6900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{6900}=\sqrt{100*69}=\sqrt{100}*\sqrt{69}=10\sqrt{69}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(10)-10\sqrt{69}}{2*20}=\frac{-10-10\sqrt{69}}{40}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(10)+10\sqrt{69}}{2*20}=\frac{-10+10\sqrt{69}}{40}
$