0=7x^2-28

Solution for 0=7x^2-28 equation:

0=7x^2-28

We move all terms to the left:

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

We add all the numbers together, and all the variables

-(7x^2-28)=0

We get rid of parentheses

-7x^2+28=0

a = -7; b = 0; c = +28;
Δ = b2-4ac
Δ = 02-4·(-7)·28
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{-(0)-28}{2*-7}=\frac{-28}{-14}
=+2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+28}{2*-7}=\frac{28}{-14}
=-2
$