(X+2)(2x-2)=90

Solution for (X+2)(2x-2)=90 equation:

(X+2)(2X-2)=90

We move all terms to the left:

(X+2)(2X-2)-(90)=0

We multiply parentheses ..

(+2X^2-2X+4X-4)-90=0

We get rid of parentheses

2X^2-2X+4X-4-90=0

We add all the numbers together, and all the variables

2X^2+2X-94=0

a = 2; b = 2; c = -94;
Δ = b2-4ac
Δ = 22-4·2·(-94)
Δ = 756
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:

$\sqrt{\Delta}=\sqrt{756}=\sqrt{36*21}=\sqrt{36}*\sqrt{21}=6\sqrt{21}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-6\sqrt{21}}{2*2}=\frac{-2-6\sqrt{21}}{4}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+6\sqrt{21}}{2*2}=\frac{-2+6\sqrt{21}}{4}
$