.(7x+2)-(3x-6)=28

Solution for .(7x+2)-(3x-6)=28 equation:

.(7x+2)-(3x-6)=28

We move all terms to the left:

.(7x+2)-(3x-6)-(28)=0

We multiply parentheses

7x^2-(3x-6)-28+=0

We get rid of parentheses

7x^2-3x+6-28+=0

We add all the numbers together, and all the variables

7x^2-3x=0

a = 7; b = -3; c = 0;
Δ = b2-4ac
Δ = -32-4·7·0
Δ = 9
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9}=3$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-3)-3}{2*7}=\frac{0}{14}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3)+3}{2*7}=\frac{6}{14}
=3/7
$