84=4x^2+20

Solution for 84=4x^2+20 equation:

84=4x^2+20

We move all terms to the left:

84-(4x^2+20)=0

We get rid of parentheses

-4x^2-20+84=0

We add all the numbers together, and all the variables

-4x^2+64=0

a = -4; b = 0; c = +64;
Δ = b2-4ac
Δ = 02-4·(-4)·64
Δ = 1024
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1024}=32$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-32}{2*-4}=\frac{-32}{-8}
=+4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+32}{2*-4}=\frac{32}{-8}
=-4
$