3x(x+7)=-36

Solution for 3x(x+7)=-36 equation:

3x(x+7)=-36

We move all terms to the left:

3x(x+7)-(-36)=0

We add all the numbers together, and all the variables

3x(x+7)+36=0

We multiply parentheses

3x^2+21x+36=0

a = 3; b = 21; c = +36;
Δ = b2-4ac
Δ = 212-4·3·36
Δ = 9
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9}=3$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-3}{2*3}=\frac{-24}{6}
=-4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+3}{2*3}=\frac{-18}{6}
=-3
$