20. Posn Math

The posn math worksheet starts with the ideas on a number line (1 dimension) and then changes over to working with posns (2 dimensions).

The important ideas are:

• Posns work a lot like numbers on the number line. Know the analogies (below).
• Think $+$ and $-$ even if you have to say posn-add and posn-subtract.
• Distance from the origin on the number line is abs; in 2d use posn-length.
• Adding $A+B$ takes a point at $A$ and moves it in direction $B$.
• Subtracting $-B+A$ or $A-B$ finds the motion from $B$ to $A$. Experiment to understand why the $B$ has the minus sign not the $A$.

Pacing: expect to be able to do and discuss the first two pages in about 45 minutes.