25=x^2+2.25x^2

Solution for 25=x^2+2.25x^2 equation:

25=x^2+2.25x^2

We move all terms to the left:

25-(x^2+2.25x^2)=0

We get rid of parentheses

-x^2-2.25x^2+25=0

We add all the numbers together, and all the variables

-3.25x^2+25=0

a = -3.25; b = 0; c = +25;
Δ = b2-4ac
Δ = 02-4·(-3.25)·25
Δ = 325
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:

$\sqrt{\Delta}=\sqrt{325}=\sqrt{25*13}=\sqrt{25}*\sqrt{13}=5\sqrt{13}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-5\sqrt{13}}{2*-3.25}=\frac{0-5\sqrt{13}}{-6.5}
=-\frac{5\sqrt{13}}{-6.5}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+5\sqrt{13}}{2*-3.25}=\frac{0+5\sqrt{13}}{-6.5}
=\frac{5\sqrt{13}}{-6.5}
$