13=5x*5x+9

Solution for 13=5x*5x+9 equation:

13=5x*5x+9

We move all terms to the left:

13-(5x*5x+9)=0

We get rid of parentheses

-5x*5x-9+13=0

We add all the numbers together, and all the variables

-5x*5x+4=0

Wy multiply elements

-25x^2+4=0

a = -25; b = 0; c = +4;
Δ = b2-4ac
Δ = 02-4·(-25)·4
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-20}{2*-25}=\frac{-20}{-50}
=2/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+20}{2*-25}=\frac{20}{-50}
=-2/5
$