Lesson plan

6. Determine the equation of a line from two points (FP)

teaches Common Core State Standards CCSS.Math.Content.8.F.B.4 http://corestandards.org/Math/Content/8/F/B/4
teaches Common Core State Standards CCSS.Math.Practice.MP6 http://corestandards.org/Math/Practice/MP6
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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 y-intercept. Algebraic equations are used here to help students focus on the procedure of calculating slope and solving for y-intercept 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 y-intercept, 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
  • y-intercept