x*x+(x*x+6)=90

Solution for x*x+(x*x+6)=90 equation:

x*x+(x*x+6)=90

We move all terms to the left:

x*x+(x*x+6)-(90)=0

Wy multiply elements

x^2+(x*x+6)-90=0

We get rid of parentheses

x^2+x*x+6-90=0

We add all the numbers together, and all the variables

x^2+x*x-84=0

Wy multiply elements

x^2+x^2-84=0

We add all the numbers together, and all the variables

2x^2-84=0

a = 2; b = 0; c = -84;
Δ = b2-4ac
Δ = 02-4·2·(-84)
Δ = 672
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:

$\sqrt{\Delta}=\sqrt{672}=\sqrt{16*42}=\sqrt{16}*\sqrt{42}=4\sqrt{42}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{42}}{2*2}=\frac{0-4\sqrt{42}}{4}
=-\frac{4\sqrt{42}}{4}
=-\sqrt{42}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{42}}{2*2}=\frac{0+4\sqrt{42}}{4}
=\frac{4\sqrt{42}}{4}
=\sqrt{42}
$