X(28-4.9x)=0

Solution for X(28-4.9x)=0 equation:

X(28-4.9X)=0

We add all the numbers together, and all the variables

X(-4.9X+28)=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{-56}{-8}
=+7
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(28)+28}{2*-4}=\frac{0}{-8}
=0
$