Equations of Straight Line Graphs

Students learn how to plot and derive the equation of straight-line graphs in the form y = mx + c.  Learning progresses on from this to find the equation of parallel and perpendicular lines in the form ax + by +c = 0.

This unit takes place in Term 3 of Year 9 and is followed by graphical functions.


Equations of Straight Line Graphs Lessons
4 Part Lesson
Plotting Straight Line Graphs
4 Part Lesson
Finding the Equation of Straight Line Graphs
4 Part Lesson
Gradient of Perpendicular Lines
4 Part Lesson
Gradient of Parallel Lines
4 Part Lesson
Gradient of Straight Line Graphs
4 Part Lesson
Plotting Straight Lines from Two Points
Additional Resources
Extended Learning
Gradient of Straight Lines
Extended Learning
Finding the equation of straight line graphs
Problem Solving
Straight Line Graphs
Revision
Perpendicular and Parallel Gradients
Revision
Plotting Straight Line Graphs
Revision
Equation of Straight Line Graphs
Prerequisite Knowledge
  • Recognise and describe linear number sequences, including those involving fractions and decimals, and find the term-to-term rule.
  • Generate and describe linear number sequences
Success Criteria
  • Plot graphs of equations that correspond to straight-line graphs in the coordinate plane;
  • Use the form y = mx + c to identify parallel lines
  • Find the equation of the line through two given points, or through one point with a given gradient
  • Identify and interpret gradients and intercepts of linear functions graphically and algebraically
Key Concepts
  • Gradient is a measure of rate of vertical change divided by horizontal change.
  • Parallel lines have the same gradient
  • The intercept always has the x value equal zero.
Common Misconceptions
  • Students often confuse linear graphs to have the same notation as statistical graphs.
  • The gradient can be calculated from any two points along the graph. Not necessarily from the origin.
  • A linear function does not have to pass through the origin.
  • It is beneficial to create a table of results when plotting a linear function. The coordinate pairs arise from the x and y values.

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