Q3 of 67 Page 86

Find the 14th and 15th triangular numbers, and find their sum. Verify the Statement 8 for this sum.

14th triangular number = 1 + 2 + 3 + 4 + … + 14 = 105


15th triangular number = 1 + 2 + 3 + 4 + … + 14 + 15 = 120


According to statement 8, the sum of nth and (n + 1)th triangular number is (n + 1)2


Here, 120 + 105 = 225


And (14 + 1)2 = 152


= 225


Hence Statement 8 is verified


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