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What is the xth triangular number?
The formula for the nth triangular number is n(n+1)/2. Therefore, the fourth triangular number is equal to 4 x (4+1) / 2 = (4 x 5) / 2 = 10. The fiftieth triangular number is equal to 50 x (50+1) / 2 = (50 x 51) / 2 = 1275.
How do you find the 20Th triangular number?
The 20th triangular number is 20*21/2 = 210
Is 9 a triangular number?
yes it is!EDIT: No, it is not.
What is the 81st triangle number?
The 81st triangular number is 3321 The nth triangular number is given by tn = n(n+1) ÷ 2 The 81st triangular number is: t81 = 81(81+1) ÷ 2 = 3321
Is 49 a triangular number?
No. ---- The nth triangular number (n must be a whole number > 0) is given by: tn = 1/2 n(n+1) Testing for 49: 1/2 n(n+1) = 49 → n2 + n - 98 = 0 → n = (-1 ± √393)/2 but 393 is not a square number, so n cannot be a whole number which it must be for a triangular number; thus 49 is not a triangular number.
