7x^2-126=-21x

Solution for 7x^2-126=-21x equation:

7x^2-126=-21x

We move all terms to the left:

7x^2-126-(-21x)=0

We get rid of parentheses

7x^2+21x-126=0

a = 7; b = 21; c = -126;
Δ = b2-4ac
Δ = 212-4·7·(-126)
Δ = 3969
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3969}=63$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-63}{2*7}=\frac{-84}{14}
=-6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+63}{2*7}=\frac{42}{14}
=3
$