x-21=1/4x

Solution for x-21=1/4x equation:

x-21=1/4x

We move all terms to the left:

x-21-(1/4x)=0


Domain of the equation: 4x)!=0

x!=0/1

x!=0

x∈R


We add all the numbers together, and all the variables

x-(+1/4x)-21=0

We get rid of parentheses

x-1/4x-21=0

We multiply all the terms by the denominator


x*4x-21*4x-1=0

Wy multiply elements

4x^2-84x-1=0

a = 4; b = -84; c = -1;
Δ = b2-4ac
Δ = -842-4·4·(-1)
Δ = 7072
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{7072}=\sqrt{16*442}=\sqrt{16}*\sqrt{442}=4\sqrt{442}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-84)-4\sqrt{442}}{2*4}=\frac{84-4\sqrt{442}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-84)+4\sqrt{442}}{2*4}=\frac{84+4\sqrt{442}}{8}
$