Idea 1of 11Builds onWhich way
Which way is plus
East or west: which one gets the plus sign?
Today you'll discover
- a choice you make once, before anything moves
- how every leg then carries its own sign
- why 'down' can be minus
Think firstBefore anything moves: east is plus
If east gets the plus sign, what does west get?
Answer first, then press Next. Read the boxed key, then each leg against it.
The dog's run drawn as legs along a ground line. First the boxed note in the corner saying east is positive. Then a key under it pairing east with plus and west with minus. Then a warm dashed arrow eight metres east labelled plus eight and a cool dashed arrow two metres back west labelled minus two, with the start-to-finish arrow at the top. The last step asks for the number a lift gets when north is plus and it goes down.
See the whole ideathe big idea and the key word, in one place
The big idea
Choose plus once. Every number then carries its own sign.
Why it happensPlus eight and minus two add to plus six: six metres east. Add the signed legs and the sign of the answer says which way it ended up.
Key word
- sign convention
- the choice, made once at the top of a problem, of which direction counts as positive
Ready to use it?
- Give each leg of a drive its sign, then add them.