Why do this problem?
is the third of three related problems. The first problem is Mirror, Mirror...
, and the second is ...on the Wall
. All three problems ask students to
consider the effect of combining two transformations, and then challenge them to describe the single transformations that produce the same results.
This problem follows on from the other two but works equally well on its own. It could be used as extension work for students learning to draw enlargements from a centre of enlargement, using fractional scale factors.
Alternatively, this problem/series of problems could provide suitable task(s) for a unit of work on combined transformations. Some knowledge of vector algebra might be useful for students attempting a full proof.
This printable resource may be useful: Who is the Fairest of Them All?.
As an extension task, all that is needed is to provide the problem as a worksheet to pairs of students who could then make sense of it together. When they have established the combined transformation for one specific example, a teacher intervention may be appropriate, to move the focus to the general case, asking the key questions below.
With a full class, encourage different students to start with different flag positions. The teacher intervention above could become a full class discussion. In theory, all students will have the same combined transformation, which should be a perfect moment for a comment on evidence versus proof.
What if the flag was in a different place?
What if you used the other point first?
What if the points were moved?
What, precisely, does the final position of the flag depend on?
Ask students to summarise their findings in exactly 20 words (!) then ask if there is anything further that might be varied.
Ask (suitably experienced) students to create a dynamic geometry file that demonstrates their findings.
Spend time drawing accurate enlargements. In theclass/groupevery enlargement could be drawn on paper with full details written on and signed; then every student could alternate between doing an enlargement and checking one off the pile.