Question

what square number will we get if add 8th and 9th triangular number​

Answer 1

Answer:

eighth and ninth triangular numbers are : 36 and 45. Now the task is pretty simple. by adding these two get 36 + 45 = 81 which is a perfect square of 9.

Answer 2

Answer:

The Triangular Number Sequence is 1, 3, 6, 10, 15, 21, 28, 36, 45 and so on. It is formed by counting the dots in a triangle. From the sequence it is evident that the 8th and the 9th number is : 36 and 45. The sum is 36 + 45 = 81 which is the square root of 9.

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