-28x+40=-4x^2

Solution for -28x+40=-4x^2 equation:

-28x+40=-4x^2

We move all terms to the left:

-28x+40-(-4x^2)=0

We get rid of parentheses

4x^2-28x+40=0

a = 4; b = -28; c = +40;
Δ = b2-4ac
Δ = -282-4·4·40
Δ = 144
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{144}=12$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-12}{2*4}=\frac{16}{8}
=2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+12}{2*4}=\frac{40}{8}
=5
$