25=9x^2+4x^2

Solution for 25=9x^2+4x^2 equation:

25=9x^2+4x^2

We move all terms to the left:

25-(9x^2+4x^2)=0

We get rid of parentheses

-9x^2-4x^2+25=0

We add all the numbers together, and all the variables

-13x^2+25=0

a = -13; b = 0; c = +25;
Δ = b2-4ac
Δ = 02-4·(-13)·25
Δ = 1300
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:

$\sqrt{\Delta}=\sqrt{1300}=\sqrt{100*13}=\sqrt{100}*\sqrt{13}=10\sqrt{13}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-10\sqrt{13}}{2*-13}=\frac{0-10\sqrt{13}}{-26}
=-\frac{10\sqrt{13}}{-26}
=-\frac{5\sqrt{13}}{-13}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+10\sqrt{13}}{2*-13}=\frac{0+10\sqrt{13}}{-26}
=\frac{10\sqrt{13}}{-26}
=\frac{5\sqrt{13}}{-13}
$