3x(X+6)=36

Solution for 3x(X+6)=36 equation:

3x(x+6)=36

We move all terms to the left:

3x(x+6)-(36)=0

We multiply parentheses

3x^2+18x-36=0

a = 3; b = 18; c = -36;
Δ = b2-4ac
Δ = 182-4·3·(-36)
Δ = 756
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:

$\sqrt{\Delta}=\sqrt{756}=\sqrt{36*21}=\sqrt{36}*\sqrt{21}=6\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-6\sqrt{21}}{2*3}=\frac{-18-6\sqrt{21}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+6\sqrt{21}}{2*3}=\frac{-18+6\sqrt{21}}{6}
$