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Per NCERT, the nth TRIANGULAR NUMBER tₙ (1, 3, 6, 10, 15, ...) equals the sum of the first n natural numbers — so the formula is which?
Atₙ = n(n + 1) / 2
Btₙ = n!
Ctₙ = 2ⁿ
Dtₙ = n²
Answer & Solution
Correct answer: A. tₙ = n(n + 1) / 2
Per NCERT §8.5, triangular number = sum of first n naturals = n(n+1)/2.
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