(2x+4)(x-16)=90

Solution for (2x+4)(x-16)=90 equation:

(2x+4)(x-16)=90

We move all terms to the left:

(2x+4)(x-16)-(90)=0

We multiply parentheses ..

(+2x^2-32x+4x-64)-90=0

We get rid of parentheses

2x^2-32x+4x-64-90=0

We add all the numbers together, and all the variables

2x^2-28x-154=0

a = 2; b = -28; c = -154;
Δ = b2-4ac
Δ = -282-4·2·(-154)
Δ = 2016
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:

$\sqrt{\Delta}=\sqrt{2016}=\sqrt{144*14}=\sqrt{144}*\sqrt{14}=12\sqrt{14}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-12\sqrt{14}}{2*2}=\frac{28-12\sqrt{14}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+12\sqrt{14}}{2*2}=\frac{28+12\sqrt{14}}{4}
$