Idea 12of 15Builds onTurn about a corner
Turn about a point outside
What if the turn point is not on the shape at all?
Today you'll discover
- how far the shape swings
- what stays the same in every turn
Think firstA triangle, and a turn point outside it
After a quarter turn clockwise about the dot, where is the triangle?
Decide first, then press Next. Watch the gap between the triangle and the dot.
Four small grids, each with a dot as the turn point and a right triangle that does not touch it, up and to the right of the dot. The others show the triangle turned 90 degrees clockwise (down and to the right), 180 degrees (down and to the left) and 90 degrees counter-clockwise (up and to the left), always the same distance from the dot.
See the whole ideathe big idea and the key word, in one place
The big idea
Every point keeps its distance from the turn point, wherever that point is.
Compare themTurn point inside: the shape spins in place. On a corner: it swings beside the point. Outside: it swings round in a wide arc.
Easy to get wrongMeasure one corner's distance to the turn point before and after. If it changed, the drawing is wrong.
Key word
- point of rotation
- the fixed point a shape turns about: inside the shape, on a corner, or outside it
Ready to use it?
- Turn a shape about a point outside it.
- Check that each corner kept its distance from the turn point.