0=7x2-28x

Solution for 0=7x2-28x equation:

0=7x^2-28x

We move all terms to the left:

0-(7x^2-28x)=0

We add all the numbers together, and all the variables

-(7x^2-28x)=0

We get rid of parentheses

-7x^2+28x=0

a = -7; b = 28; c = 0;
Δ = b2-4ac
Δ = 282-4·(-7)·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*-7}=\frac{-56}{-14}
=+4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(28)+28}{2*-7}=\frac{0}{-14}
=0
$