-2x(x+7)=0

Solution for -2x(x+7)=0 equation:

-2x(x+7)=0

We multiply parentheses

-2x^2-14x=0

a = -2; b = -14; c = 0;
Δ = b2-4ac
Δ = -142-4·(-2)·0
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-14)-14}{2*-2}=\frac{0}{-4}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-14)+14}{2*-2}=\frac{28}{-4}
=-7
$