9r^2=-81r

Solution for 9r^2=-81r equation:

9r^2=-81r

We move all terms to the left:

9r^2-(-81r)=0

We get rid of parentheses

9r^2+81r=0

a = 9; b = 81; c = 0;
Δ = b2-4ac
Δ = 812-4·9·0
Δ = 6561
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{6561}=81$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(81)-81}{2*9}=\frac{-162}{18}
=-9
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(81)+81}{2*9}=\frac{0}{18}
=0
$