Question

find the sum of the first 22 terms of the A.P: 7 ,2,-3....
Here a=7, d= -4 n=22 sn= ?
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Answer 1

Given:

• a = 7
• d = - 4
• n = 22

Find:

• Sum of first of 22 terms

Solution:

We Know,

• Sum = n/2 [2a + (n - 1) d]

Let's Start -

➤ n/2 [2a + (n - 1) d]

➤ 22/2 [2 ༝ 7 + (22 - 1) ༝ (- 4)]

➤ 22/2 [2 ༝ 7 + 21 ༝ (- 4)]

➤ 22/2 [2 ༝ 7 - 84]

➤ 22/2 [14 - 84]

➤ 22/2 [- 70]

➤ 11 ༝ [- 70]

➤ - 770

• Hence, the sum of first 22 terms of A.P is -770.