median
don steward
mathematics teaching 10 ~ 16

Sunday, 8 May 2016

triangular prisms

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









Saturday, 7 May 2016

subtracting fractions

sometimes it is good to present tasks without talking too much, so that students do the work...

you could show these particular subtractions and ask students to work out                          
(a) what the question is and
(b) what is going on

this enables the teacher to drink their tea









Friday, 6 May 2016

bike stand algebra

students can find general rules and possibly find the value for the next bike stand in the sequence
fairly realistic data - only tweaked slightly...

all are the same width and height



Monday, 2 May 2016

length, area and volume factors

it's probably helpful if students appreciate what happens to the overall size of a shape if you double in two or three directions*

























see also big sprouts and Frodo Baggins
and wombats and diprotodons 

*an estimate of the adult height of a male is double their height when they are 2 years old
for a female it is double their height at 18 months

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 ppt 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