M4.8.4 For the adult
Equations of straight lines
A straight line goes through (1, 3) and (4, 9). How do I find its equation?
What this chapter teaches
The gradient of a line is the rise divided by the run, and y = mx + c has the gradient m. Parallel lines have equal gradients. Perpendicular lines have gradients that multiply to −1.
Three questions to ask
There is no one right wording. Listen for the idea.
- How do you find the gradient of a line from two points on it?
- How do you use one point to find c in y = mx + c?
- If one line has gradient 2, what are the gradients of a parallel line and a perpendicular line?
After the chapter, the learner can
- Find the equation of a line through two points
- Spot parallel and perpendicular lines from their gradients
What they copy into their notebook
Gradient m = rise ÷ run. Put one point in y = mx + c to find c. Parallel: same m. Perpendicular: the m values multiply to −1.