2(x+5)(x-3)-x(x+5)=90

Solution for 2(x+5)(x-3)-x(x+5)=90 equation:

2(x+5)(x-3)-x(x+5)=90

We move all terms to the left:

2(x+5)(x-3)-x(x+5)-(90)=0

We multiply parentheses

-x^2+2(x+5)(x-3)-5x-90=0

We multiply parentheses ..

-x^2+2(+x^2-3x+5x-15)-5x-90=0

We add all the numbers together, and all the variables

-1x^2+2(+x^2-3x+5x-15)-5x-90=0

We multiply parentheses

-1x^2+2x^2-6x+10x-5x-30-90=0

We add all the numbers together, and all the variables

x^2-1x-120=0

a = 1; b = -1; c = -120;
Δ = b2-4ac
Δ = -12-4·1·(-120)
Δ = 481
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-\sqrt{481}}{2*1}=\frac{1-\sqrt{481}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{481}}{2*1}=\frac{1+\sqrt{481}}{2}
$