26=r^2+11r

Solution for 26=r^2+11r equation:

26=r^2+11r

We move all terms to the left:

26-(r^2+11r)=0

We get rid of parentheses

-r^2-11r+26=0

We add all the numbers together, and all the variables

-1r^2-11r+26=0

a = -1; b = -11; c = +26;
Δ = b2-4ac
Δ = -112-4·(-1)·26
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-11)-15}{2*-1}=\frac{-4}{-2}
=+2
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-11)+15}{2*-1}=\frac{26}{-2}
=-13
$