Lesson objective: Determine the equation of a line given two points, including vertical and horizontal lines.
This lesson helps to build procedural skill with slope calculation and solving for the yintercept. Algebraic equations are used here to help students focus on the procedure of calculating slope and solving for yintercept when it is not easy to reason through these components using a graph, table, or verbal description. This work develops students' understanding that the slope is equivalent between all pairs of points on a given line, so only two points are needed to define a linear function.
Students engage in Mathematical Practice 6 (Attend to precision) as they calculate slope and yintercept, being careful to adhere strictly to the definition of slope, and not mix up the x and y values, or the order of their values when calculating differences.
Key vocabulary:
 horizontal line
 slope
 undefined slope
 vertical line

yintercept