We can use the formula for the nth term of an arithmetic progression to solve this problem. The formula is:
an = a1 + (n-1)d
where an is the nth term, a1 is the first term, n is the number of terms, and d is the common difference.
We know that a1 = -11 and a5 = 1. We can use these values to find the common difference:
a5 = a1 + (5-1)d
1 = -11 + 4d
d = 3
Now that we know the common difference, we can find the sum of the first eight terms using the formula:
Sn = n/2[2a1 + (n-1)d]
Substituting the values we know:
S8 = 8/2[2(-11) + (8-1)(3)]
S8 = 4[-22 + 21]
S8 = -4
Therefore, the sum of the first eight terms is -4.
If the first term of an Ap is -11 and the fifth term is 1. What is the sum of the first eight terms?
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