Question
Without drawing a diagram, find. 6th triangular number.
✓
Answer
A triangular number can easily be remembered by the following rule
$N^{th}$ triangular number,
$= n \times ( n + 1 )2$ Therefore,
$6^{th}$ triangular number,
$= 6 \times (6 + 1)2 = 21$
$N^{th}$ triangular number,
$= n \times ( n + 1 )2$ Therefore,
$6^{th}$ triangular number,
$= 6 \times (6 + 1)2 = 21$
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