Mathematics

The sum of the first n terms of the arithmetic progression 5, 11, 17, 23,…

The sum of the first n terms of the arithmetic progression 5, 11, 17, 23, 29, 35, … is
  • A.
    n(3n – 0.5)
  • B.
    n(3n + 2)
  • C.
    n(3n + 2.5)
  • D.
    n(3n + 5)
Correct Answer: Option B
Explanation

a = 5, d = 6, n = n
Sn = n/2(2a + (n-1)d)
= n/2(2(5) + (n-1)6)
= n/2(10 + 6n-6)
= n/2(6n+4)
= 6n2/2 + 4n/2
= 32 + 2n
= n(3n + 2)