-28=-7(3x-4)21x

Solution for -28=-7(3x-4)21x equation:

-28=-7(3x-4)21x

We move all terms to the left:

-28-(-7(3x-4)21x)=0


We calculate terms in parentheses: -(-7(3x-4)21x), so:

-7(3x-4)21x

We multiply parentheses

-441x^2+588x

Back to the equation:

-(-441x^2+588x)


We get rid of parentheses

441x^2-588x-28=0

a = 441; b = -588; c = -28;
Δ = b2-4ac
Δ = -5882-4·441·(-28)
Δ = 395136
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{395136}=\sqrt{28224*14}=\sqrt{28224}*\sqrt{14}=168\sqrt{14}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-588)-168\sqrt{14}}{2*441}=\frac{588-168\sqrt{14}}{882}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-588)+168\sqrt{14}}{2*441}=\frac{588+168\sqrt{14}}{882}
$