7x^2-28+21=0

Solution for 7x^2-28+21=0 equation:

7x^2-28+21=0

We add all the numbers together, and all the variables

7x^2-7=0

a = 7; b = 0; c = -7;
Δ = b2-4ac
Δ = 02-4·7·(-7)
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-14}{2*7}=\frac{-14}{14}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+14}{2*7}=\frac{14}{14}
=1
$