7(x+1)(4x-8)=0

Solution for 7(x+1)(4x-8)=0 equation:

7(x+1)(4x-8)=0

We multiply parentheses ..

7(+4x^2-8x+4x-8)=0

We multiply parentheses

28x^2-56x+28x-56=0

We add all the numbers together, and all the variables

28x^2-28x-56=0

a = 28; b = -28; c = -56;
Δ = b2-4ac
Δ = -282-4·28·(-56)
Δ = 7056
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{7056}=84$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-84}{2*28}=\frac{-56}{56}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+84}{2*28}=\frac{112}{56}
=2
$