Question

Without drawing a diagram, find

(i) 10th square number
(ii) 6th triangular number.

Answer 1

(i) 10^th square number: A square number can easily be remembered by the following rule:
n^th square number = n²
∴ 10^th square number = 10² = 100

(ii) 6^th triangular number: A triangular number can easily be remembered by the following rule:
n^th triangular number = $\frac{n\times (n+1)}{2}$
∴ 6^th triangular number = $\frac{6\times (6+1)}{2}$ = 21