25-r^2=9r

Solution for 25-r^2=9r equation:

25-r^2=9r

We move all terms to the left:

25-r^2-(9r)=0

We add all the numbers together, and all the variables

-1r^2-9r+25=0

a = -1; b = -9; c = +25;
Δ = b2-4ac
Δ = -92-4·(-1)·25
Δ = 181
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-\sqrt{181}}{2*-1}=\frac{9-\sqrt{181}}{-2}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+\sqrt{181}}{2*-1}=\frac{9+\sqrt{181}}{-2}
$