Question 106851
An {{{one}}}{{{ variable}}} equation is a {{{line}}} in a {{{two-dimensional}}} "space". 

Example: {{{x – 5 = 3}}}   =>   {{{x = 8}}} this represents a {{{line}}} {{{parallel}}} to {{{y-axis}}} that start from the number {{{x=8}}}. In fact it is a {{{constant}}} number.

Now, if u have a {{{two}}}{{{ variable}}} equation like {{{y + x = 1}}} => {{{y = -x +1}}} it represents the {{{linear }}}{{{equation}}}(also a line) in {{{two-dimensional}}} space.
however, a two variable equation doesn’t have always to represent a line, it could represent quadratic equation, or circle (which make them different to one variable equations) like this equations:
{{{x^2+y^2=16}}} is a two variable equation too, but now represents a circle.
{{{  y=x^2 }}} represents the quadratic equation (the graph is a parabola) in two-dimensional space.



 conclusion:
one-variable equation is  representating of a number (2D)
two-variables  equation is representing curves in two dimensions (2D)