3x(x+3)=36

Solution for 3x(x+3)=36 equation:

3x(x+3)=36

We move all terms to the left:

3x(x+3)-(36)=0

We multiply parentheses

3x^2+9x-36=0

a = 3; b = 9; c = -36;
Δ = b2-4ac
Δ = 92-4·3·(-36)
Δ = 513
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{513}=\sqrt{9*57}=\sqrt{9}*\sqrt{57}=3\sqrt{57}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-3\sqrt{57}}{2*3}=\frac{-9-3\sqrt{57}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+3\sqrt{57}}{2*3}=\frac{-9+3\sqrt{57}}{6}
$