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'Triangles Within Pentagons' printed from https://nrich.maths.org/
Having identified the rule is it possible to work backwards and reconstruct pentagons using the triangular numbers?
This problem builds on the work of the three problems "
sequences and series
", "
triangles within triangles
" and "
triangles within squares
".
There are many more patterns and relationships involving triangular numbers and some experimentation could result in some pupil generated discoveries.