(2x+10)(2x-10)=90

Solution for (2x+10)(2x-10)=90 equation:

(2x+10)(2x-10)=90

We move all terms to the left:

(2x+10)(2x-10)-(90)=0

We use the square of the difference formula

4x^2-100-90=0

We add all the numbers together, and all the variables

4x^2-190=0

a = 4; b = 0; c = -190;
Δ = b2-4ac
Δ = 02-4·4·(-190)
Δ = 3040
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:

$\sqrt{\Delta}=\sqrt{3040}=\sqrt{16*190}=\sqrt{16}*\sqrt{190}=4\sqrt{190}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{190}}{2*4}=\frac{0-4\sqrt{190}}{8}
=-\frac{4\sqrt{190}}{8}
=-\frac{\sqrt{190}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{190}}{2*4}=\frac{0+4\sqrt{190}}{8}
=\frac{4\sqrt{190}}{8}
=\frac{\sqrt{190}}{2}
$