What are two ways to distinguish the differences between non-linear and linear relationships?

I know one of them has to do with first differences, what about the second?What are two ways to distinguish the differences between non-linear and linear relationships?
write the equation of the graph.


If it is in standard form (number times x + number times y = number) or slope-intercept form (y = number + or - number times x) then it is linear.


If there are any exponents shown in the equation, then it is not linear. If x and y are being multiplied together, then it is non-linear


examples:


2x + 6y = 6 %26lt;--- standard form


y = 5x - 3 or y = 1/6x + 4 %26lt;----- slope intercept form





2xy - 8 = 15-- nonlinear equations


x^2 +5y = 26 /