r+r2=18

Solution for r+r2=18 equation:

r+r2=18

We move all terms to the left:

r+r2-(18)=0

We add all the numbers together, and all the variables

r^2+r-18=0

a = 1; b = 1; c = -18;
Δ = b2-4ac
Δ = 12-4·1·(-18)
Δ = 73
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{-(1)-\sqrt{73}}{2*1}=\frac{-1-\sqrt{73}}{2}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{73}}{2*1}=\frac{-1+\sqrt{73}}{2}
$