4x(X+7)=56

Solution for 4x(X+7)=56 equation:

4x(x+7)=56

We move all terms to the left:

4x(x+7)-(56)=0

We multiply parentheses

4x^2+28x-56=0

a = 4; b = 28; c = -56;
Δ = b2-4ac
Δ = 282-4·4·(-56)
Δ = 1680
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:

$\sqrt{\Delta}=\sqrt{1680}=\sqrt{16*105}=\sqrt{16}*\sqrt{105}=4\sqrt{105}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(28)-4\sqrt{105}}{2*4}=\frac{-28-4\sqrt{105}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(28)+4\sqrt{105}}{2*4}=\frac{-28+4\sqrt{105}}{8}
$