Question

In an A.P., the first term is 22, nth term is -11 and the sum to first n terms is 66. Find n and d, the common difference.

Answer 1

Answer:

use this formula Sn=n/2[2a+(n-1)d]

Answer 2

n = 12, d = -3

Step-by-step explanation:

(i) Given: In an A.P., the first term is 22, nth term is -11 and the sum to first n terms is 66.  

Find: n and d

  a = 22

  Sum = 66

  an = -11 = a + (n-1)d

  So 2a + (n-1)d = an + a = -11 + 22 = +11

  Now Sum = n/2 (2a + (n-1)d)

  66 = n/2 (11)

  n = 66 *2 / 11

  n = 12

  Substituting n in an, we get: 22 + 11d = -11

   11d = -33

    d = -3

  AP will be 22, 19, 16, 13, 10, 7, 4, 1, -2, -5, -8, -11.