Question

Find the sum of first n terms.

(a) \(\frac{n(n+1)}{2}\)

(b) \((\frac{n(n+1)}{2})^3\)

(c) \(\frac{n(n+1)(2n+1)}{6}\)

(d) \((\frac{n(n+1)}{2})^2\)

The question was asked during an online interview.

My doubt is from Sum to n Terms of Special Series topic in portion Sequences and Series of Mathematics – Class 11

Answer 1

Correct choice is (a) \(\frac{n(n+1)}{2}\)

The explanation is: Sum of first n terms = 1+2+3+4+……+n

=> (n/2) (a + an) = (n/2) (1+n) = \(\frac{n(n+1)}{2}\).