M4.2.7 For the adult
Graphs of proportion
How can I tell from a graph that two amounts are in proportion?
What this chapter teaches
Direct proportion y = kx makes a straight line through the origin, and k is the gradient. Inverse proportion y = k ÷ x makes a curve that falls and never touches the axes. From a table, y ÷ x fixed means direct and x × y fixed means inverse.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why must a graph of direct proportion pass through the origin?
- How can you tell from a table of values whether two amounts are inversely proportional?
- Why is the line y = 2x + 3 not a graph of proportion?
After the chapter, the learner can
- Sketch the graphs of y = kx and y = k/x
- Spot direct or inverse proportion from a table or graph
What they copy into their notebook
The graph of y = kx is a straight line through the origin. The graph of y = k ÷ x is a curve that never touches the axes. A table: y ÷ x fixed is direct, x × y fixed is inverse.