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

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

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

We add all the numbers together, and all the variables

4x(-1x-7)=0

We multiply parentheses

-4x^2-28x=0

a = -4; b = -28; c = 0;
Δ = b2-4ac
Δ = -282-4·(-4)·0
Δ = 784
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{784}=28$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-28}{2*-4}=\frac{0}{-8}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+28}{2*-4}=\frac{56}{-8}
=-7
$