Writing about similar triangles

Here is an example of a calculation and writing task.

In the following set of triangles, which one is not similar to the other three? Write an explanation with your answer.

Four triangles of different sizes, each labelled with two interior angles.

Similar or not?

When asking students to complete questions like this, make it clear that you expect not only answers but also written reasons for each response. It will take students longer, but you will be able to see and evaluate their levels of thinking about set tasks.

Curriculum links

Year 9: Use the enlargement transformation to explain similarity and develop the conditions for triangles to be similar

Year 10: Formulate proofs involving congruent triangles and angle properties

Year 10: Apply logical reasoning, including the use of congruence and similarity, to proofs and numerical exercises involving plane shapes