An AP has first term 4 and common difference 6. Which expression gives S_n , the sum of its first n terms?

Question

Accepted Answer

3n^2 + n. S_n = n/2[2(4) + 6(n-1)] = n/2[2 + 6n] = n(1 + 3n) = 3n^2 + n. (Check: S_1 = 4 = a and S_2 = 14 = 4 + 10.) The option 3n^2 + 4n uses 6n instead of 6(n-1) in the bracket. 3n^2 + n/2 halves once too often, since the n/2 has already been used. 6n^2 + 2n never halves at all.

An AP has first term 4 and common difference 6. Which expression gives $S_{n}$ , the sum of its first $n$ terms?

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More Class 10 Sum of n Terms of an AP practice

An AP has first term 4 and common difference 6. Which expression gives Sn​, the sum of its first n terms?

Step-by-Step Solution

Master this chapter in 30 minutes a day.

More Class 10 Sum of n Terms of an AP practice

An AP has first term 4 and common difference 6. Which expression gives $S_{n}$ , the sum of its first $n$ terms?