# ICSE Class 10 Answered

**In arithmetic progression , when we use s=n/2 [2a+(n-1)d] then why use a=(n-1)d formula?**

Asked by rashikulkarni28 | 14 Aug, 2022, 04:30: PM

Expert Answer

In the formula S = n/2(2a + (n-1)d)

We have a as the first term

Second term = a+d

Third term = 2a+d

Fourth term = 3a+d

.

.

.

Nth term = (n-1)a + d

Sum of n terms is S = a + a+d + 2a+d + 3a+d + ... + (n-1)a = n/2(2a + (n-1)d)

Answered by Renu Varma | 15 Aug, 2022, 10:11: AM

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