X(x+4)=81+4x

Solution for X(x+4)=81+4x equation:

X(X+4)=81+4X

We move all terms to the left:

X(X+4)-(81+4X)=0

We add all the numbers together, and all the variables

X(X+4)-(4X+81)=0

We multiply parentheses

X^2+4X-(4X+81)=0

We get rid of parentheses

X^2+4X-4X-81=0

We add all the numbers together, and all the variables

X^2-81=0

a = 1; b = 0; c = -81;
Δ = b2-4ac
Δ = 02-4·1·(-81)
Δ = 324
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{324}=18$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-18}{2*1}=\frac{-18}{2}
=-9
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+18}{2*1}=\frac{18}{2}
=9
$