36=a^2+9a

Solution for 36=a^2+9a equation:

36=a^2+9a

We move all terms to the left:

36-(a^2+9a)=0

We get rid of parentheses

-a^2-9a+36=0

We add all the numbers together, and all the variables

-1a^2-9a+36=0

a = -1; b = -9; c = +36;
Δ = b2-4ac
Δ = -92-4·(-1)·36
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-15}{2*-1}=\frac{-6}{-2}
=+3
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+15}{2*-1}=\frac{24}{-2}
=-12
$