0=4x^2-16x-84

Solution for 0=4x^2-16x-84 equation:

0=4x^2-16x-84

We move all terms to the left:

0-(4x^2-16x-84)=0

We add all the numbers together, and all the variables

-(4x^2-16x-84)=0

We get rid of parentheses

-4x^2+16x+84=0

a = -4; b = 16; c = +84;
Δ = b2-4ac
Δ = 162-4·(-4)·84
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-40}{2*-4}=\frac{-56}{-8}
=+7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+40}{2*-4}=\frac{24}{-8}
=-3
$