Question

(i) In an airthmetic progression d = -4, n = 7 and S,
4. then the value of a will be..​

Answer 1

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Given : a = first term

            d = common difference = -4

            Sn = sum of all terms =4

             n = total no of terms = 7

now using Sn formula,

Sn = n/2 x (2a + (n-1)d )

=> S7 = 7/2 x (2a + 6d)

4 = 7/2 x (2a +  -24)

8 = 7 (2a-24)

8 = 14a - 168

14a = 176

a = 176/14

a = 88/7

hence the first term is 88/7.

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