Practice variation 2 of 3
Combinatorics — A sum of first-column diagonals
Your question
(i) Use Pascal’s identity to show .
(ii) Hence evaluate .
This practice question was inspired by Question 13(e) in the 2025 NSW HSC Mathematics Extension 1 examination, © NESA. It is an original TestMum variation that practises the same mathematical idea, not an official NESA question.
Before you check
- Have you stated every choice or assumption?
- Can another student follow each line?
- Did you verify the final result independently?