Non Linear

This produces a curve
ax2 + by2 = c

Trigonometric Functions

Quadratic

3x2 - 2y = 7

Exponential

Produces an exponential curve that best fits a set of data that does not change linearly with time
For example a series of population growth will always be better represented with an exponential curve

Power

Logarithm

Cubic

x3 - x2 + x = 4