**Geometry Chapter 3.6 Parallel lines in the Coordinate Plane**

**I) Vocabulary:**

**A) Slope**: (nonvertical line): Ratio of the vertical change (the rise, Δ y) to the horizontal change (the run, Δ x)

**Formula**: slope = m = (Δy/Δx) = (y

_{2}- y

_{1})÷ (x

_{2}- x

_{2})

**II) Postulate:**

A) In the coordinate plane, 2 nonvertical lines are parallel if and only if they have the same slope. Any two vertical or horizontal lines are parallel.

B) Equation of a line:

y = mx + b

where m is the slope of the line and b is the y-intersept (where it crosses the y-axis)