r^2+8r=-15r

Solution for r^2+8r=-15r equation:

r^2+8r=-15r

We move all terms to the left:

r^2+8r-(-15r)=0

We get rid of parentheses

r^2+8r+15r=0

We add all the numbers together, and all the variables

r^2+23r=0

a = 1; b = 23; c = 0;
Δ = b2-4ac
Δ = 232-4·1·0
Δ = 529
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{529}=23$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(23)-23}{2*1}=\frac{-46}{2}
=-23
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(23)+23}{2*1}=\frac{0}{2}
=0
$