x^2-18x+81=4x^2

Solution for x^2-18x+81=4x^2 equation:

x^2-18x+81=4x^2

We move all terms to the left:

x^2-18x+81-(4x^2)=0

determiningTheFunctionDomain
x^2-4x^2-18x+81=0

We add all the numbers together, and all the variables

-3x^2-18x+81=0

a = -3; b = -18; c = +81;
Δ = b2-4ac
Δ = -182-4·(-3)·81
Δ = 1296
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1296}=36$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-18)-36}{2*-3}=\frac{-18}{-6}
=+3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-18)+36}{2*-3}=\frac{54}{-6}
=-9
$