M3.9.7 For the adult
The equation y = mx + c
Can I see how steep a line is, and where it crosses, from its rule alone?
What this chapter teaches
A straight line has an equation y = mx + c. The number m is its gradient and the number c is where it crosses the y axis. Lines with the same m are parallel. You can write the equation from a graph by reading c and finding rise ÷ run.
Three questions to ask
There is no one right wording. Listen for the idea.
- In y = 5x + 2, what are m and c?
- How do you know the line y = 5x + 2 crosses the y axis at (0, 2)?
- How can you tell that y = 3x + 1 and y = 3x − 4 are parallel?
After the chapter, the learner can
- Find the gradient of y = 3x − 2 from its equation
- Find where y = 3x − 2 crosses the y axis
- Write the equation of a line from its graph
What they copy into their notebook
y = mx + c. The number m in front of x is the gradient. The number c on its own is where the line crosses the y axis, at (0, c). Parallel lines have the same m.