4x^2-84=400

Solution for 4x^2-84=400 equation:

4x^2-84=400

We move all terms to the left:

4x^2-84-(400)=0

We add all the numbers together, and all the variables

4x^2-484=0

a = 4; b = 0; c = -484;
Δ = b2-4ac
Δ = 02-4·4·(-484)
Δ = 7744
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{7744}=88$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-88}{2*4}=\frac{-88}{8}
=-11
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+88}{2*4}=\frac{88}{8}
=11
$