Question 14015
Any easy way to look at an equation and know if it is linear or not is to look at the degree of the function.  The degree is simple the exponent of x.  For example the function y={{{x^2}}} is  a function of degree 2. y={{{3x^3+24}}}is a function fo degree 3.  Linear functions are functions that have a degree of one, that is, f(x)= mx+b where x,b are constants.  A function with a higher degree will not be linear here's some graphs to illustrate.

y=x
{{{graph(300,200,-10,10,-10,10,x)}}}.

y={{{x^2}}}
{{{graph(300,200,-10,10,-10,10,x^2)}}}.

y={{{x^3}}}
{{{graph(300,200,-10,10,-10,10,x^3)}}}

y={{{x^4}}}
{{{graph(300,200,-10,10,-10,10,x^4)}}}

y={{{x^5}}}
{{{graph(300,200,-10,10,-10,10,x^5)}}}

Hope this helps