2x^2+4x^2=90

Solution for 2x^2+4x^2=90 equation:

2x^2+4x^2=90

We move all terms to the left:

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

We add all the numbers together, and all the variables

6x^2-90=0

a = 6; b = 0; c = -90;
Δ = b2-4ac
Δ = 02-4·6·(-90)
Δ = 2160
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:

$\sqrt{\Delta}=\sqrt{2160}=\sqrt{144*15}=\sqrt{144}*\sqrt{15}=12\sqrt{15}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-12\sqrt{15}}{2*6}=\frac{0-12\sqrt{15}}{12}
=-\frac{12\sqrt{15}}{12}
=-\sqrt{15}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+12\sqrt{15}}{2*6}=\frac{0+12\sqrt{15}}{12}
=\frac{12\sqrt{15}}{12}
=\sqrt{15}
$