Question

formula to be used to find sum of n-1 of an AP​

Answer 1

Answer:

The sum of n terms of AP is the sum(addition) of first n terms of the arithmetic sequence. It is equal to n divided by 2 times the sum of twice the first term – 'a' and the product of the difference between second and first term-'d' also known as common difference, and (n-1), where n is numbers of terms to be added.

Answer 2

Answer:

n/2{2a+(n-1)d} is the formula used to find the sum up to nth term