median
don steward
mathematics teaching 10 ~ 16

Sunday, 24 April 2016

combined enlargements

what happens (in general) if you do one enlargement scale factor 2 from one centre and then enlarge the resultant shape from another centre, also scale factor 2?

the powerpoint is here
it needs to be downloaded for the animations to work

enlarge the brown triangle, scale factor 2, to obtain the blue triangle


then enlarge the blue triangle from a different centre, to obtain the red triangle

the two enlargements, one after the other

students could either do their own or use these resources


















the third triangle can also be obtained from the first via an enlargement

what will the scale factor be and where will the centre of enlargement be?

it seems as if the three centres have some relationship

check this with the ones drawn above
















what happens with different scale factors?






















the proof of the relationship can be done using vectors

this was done by James Pearce, of Mathspad fame

many thanks for the very neat vector proof, which he did generalise



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