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


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.
  • Linear Graphs
  • 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.

 

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes:

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Mr Mathematics Blog

Sharing an Amount to a Given Ratio

There are three common methods for sharing an amount to a given ratio.  Depending on the age group and ability range I am teaching I would choose one approach over the other two. The three methods are: Using fractions Unitary method Using a table In this blog I will demonstrate each of the three methods […]

Plotting Scatter Graphs and Understanding Correlation

To introduce plotting scatter graphs and understanding correlation I ask students to think about the relationships between different variables and to describe how they might be related. Here’s my starter activity which students discuss in pairs then present to me on mini-whiteboards. When the students have had time to discuss the matching pairs we talk […]

Plotting Quadratic Graphs on Cartesian Axes

In recent examiner reports it is noted how important it is for students to understand the properties of a parabola  when plotting quadratic graphs on Cartesian axes.  Students who have a secure understanding of parabolas can use them to correct miscalculated values in their table of results and are more likely to attain full marks […]