-28x=4x^2

Solution for -28x=4x^2 equation:

-28x=4x^2

We move all terms to the left:

-28x-(4x^2)=0

determiningTheFunctionDomain
-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
$