Mathematics

Without using a diagram, find:
(i) 9^th square number
(ii) 7^th triangular number

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(i) The n^th square number is given by n × n = n².

So, the 9^th square number = 9 × 9 = 9² = 81.

(ii) The n^th triangular number is given by $\dfrac{n(n+1)}{2}$ .

So, the 7^th triangular number = $\dfrac{7 \times (7+1)}{2}$ = $\dfrac{7 \times 8}{2}$ = $\dfrac{56}{2}$ = 28.

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