a3 = a1 + 2d
a9 = a1 + 8d
a3 + a9 = 2a1 + 10d = a1 + a11 = 8
sum of a1 + ... + a11 = (11/2)(a1 + a11) = (11/2)*8 = 44
Krista H.
asked 09/15/19So this is my math problem:
In the arithmetic sequence is a3 + a9 = 8. Find the sum of the first 11 members of the sequence.
a3 = a1 + 2d
a9 = a1 + 8d
a3 + a9 = 2a1 + 10d = a1 + a11 = 8
sum of a1 + ... + a11 = (11/2)(a1 + a11) = (11/2)*8 = 44
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