Question

The sum of first n terms of an A.P. is 5n – n². Find the nth term of this A.P.

Answer 1

  an  = 6-2n

Step-by-step explanation:

(i) Given: The sum of first n terms of an A.P. is 5n – n²

Find: nth term of this A.P.

  Now Sum = 5n – n²

  S1 = 5(1) -(1)² = 4 = a1

  S2 = 5(2) -4 = 6

  S2 - S1 = a2 = 2

  So d = 2-4 = -2

  We have a = 4, d = -2

  an = a + (n-1)d  

    = 4 + (n-1)(-2)

    = 4 -2n +2

  an  = 6-2n