A parent graph is the basic representation of a function. In Chapter 2, you are learning about linear functions f(x) = x which is a straight line passing through the origin with a slope of 1. All lines are a variation of this parent function created by multiplying x by a constant (changing the slope) or adding/subtracting a constant (changing the y-axis intercept). It goes without saying, that all lines are straight.

A group of lines having the same slope (but diferent y-axis intercepts) form a subfamily of parallel lines.

Horizontal lines (slope equaling zero) form another subfamily. These lines are called constant functions since f(x), aka y, always has the same constant value, regardless of the value of x.

Practice your understanding by sketching on co-ordinate planes a family of parallel lines and a family of horizontal lines. State each line's equation.