84=(2x+2)x

Solution for 84=(2x+2)x equation:

84=(2x+2)x

We move all terms to the left:

84-((2x+2)x)=0


We calculate terms in parentheses: -((2x+2)x), so:

(2x+2)x

We multiply parentheses

2x^2+2x

Back to the equation:

-(2x^2+2x)


We get rid of parentheses

-2x^2-2x+84=0

a = -2; b = -2; c = +84;
Δ = b2-4ac
Δ = -22-4·(-2)·84
Δ = 676
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{676}=26$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-26}{2*-2}=\frac{-24}{-4}
=+6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+26}{2*-2}=\frac{28}{-4}
=-7
$