4x^2+x^2=90

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

4x^2+x^2=90

We move all terms to the left:

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

We add all the numbers together, and all the variables

5x^2-90=0

a = 5; b = 0; c = -90;
Δ = b2-4ac
Δ = 02-4·5·(-90)
Δ = 1800
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:

$\sqrt{\Delta}=\sqrt{1800}=\sqrt{900*2}=\sqrt{900}*\sqrt{2}=30\sqrt{2}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-30\sqrt{2}}{2*5}=\frac{0-30\sqrt{2}}{10}
=-\frac{30\sqrt{2}}{10}
=-3\sqrt{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+30\sqrt{2}}{2*5}=\frac{0+30\sqrt{2}}{10}
=\frac{30\sqrt{2}}{10}
=3\sqrt{2}
$