1. Section 1.2
Relations

2. Relation
Relation is a set of points in the plane (graphical description)
Roster method lists all of the points which belong to the relation R
We write:
R = { (-2,1),(4,3), (0,-3) }
Roster description
Graphical description

3. Example Graph the following relations
HLS1 = { (x, 3) : -2 ≤ x ≤ 4}
HLS2 = { (x, 3) : -2 ≤ x < 4}
V = { (3, y): y is a real number}

4. Algebraic Description
We can describe the points in V as those points which satisfy the equation x = 3
The equation y = -2 corresponds to all points in the plane whose y-coordinate is -2

5. Equations of Vertical and Horizontal Lines
The graph of the equation x = a is a vertical line through (a,0)
The graph of the equation y = b is a horizontal line through (0,b)

6. Example
Graph the relation: R = { (x,y) : 1 < y ≤ 3 }