37. Find the sum of first 22 terms of an AP in which third term is 7 and seventh term is 2 more than thrice of its third term.​

1 thought on “37. Find the sum of first 22 terms of an AP in which third term is 7 and seventh term is 2 more than thrice of its third term.​”

1. Question:–

   Find the sum of first 22 terms of an AP in which third term is 7 and seventh term is 2 more than thrice of its third term.

   Answer:–

   Given:

   • a3 = 7
   • a7 = 3a3 + 2

   To find:–

   • Sum of first 22 sums.

   ________________

   • a + 2d = 7
   • a + 6d = 3 (a+2d) + 2
   • Here a is -1
   • a = -1 , d = 4

   ————————

   ➦ Sn = n/2 [2a + ( n-1 ) d]

   ➦ Sn = 22/2 [ 2(-1) + (22-1) x 4]

   ➦ Sn = 11 [ -2 + 44 ]

   ➦ Sn = 242

   So sum of first 22 terms is 242.

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