M4.8.2 For the adult
Changing the subject
The formula v = u + at gives speed. How do I get t on its own?
What this chapter teaches
A formula is a machine. To make a different letter the subject, undo its steps in reverse order and do the same to both sides. A letter that appears twice is collected on one side and factorised out.
Three questions to ask
There is no one right wording. Listen for the idea.
- In v = u + at, which step happens last, and so which do you undo first?
- Why can you not divide both sides by a if a might be zero?
- How can you check a rearranged formula by putting in numbers?
After the chapter, the learner can
- Rearrange v = u + at to make t the subject
- Rearrange a formula where the subject appears twice
What they copy into their notebook
Undo the steps in reverse order, doing the same to both sides. If the subject is in two terms, collect them and factorise. Never divide by zero.