-4x(x+7)=36

Solution for -4x(x+7)=36 equation:

-4x(x+7)=36

We move all terms to the left:

-4x(x+7)-(36)=0

We multiply parentheses

-4x^2-28x-36=0

a = -4; b = -28; c = -36;
Δ = b2-4ac
Δ = -282-4·(-4)·(-36)
Δ = 208
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:

$\sqrt{\Delta}=\sqrt{208}=\sqrt{16*13}=\sqrt{16}*\sqrt{13}=4\sqrt{13}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-4\sqrt{13}}{2*-4}=\frac{28-4\sqrt{13}}{-8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+4\sqrt{13}}{2*-4}=\frac{28+4\sqrt{13}}{-8}
$