# math

posted by mpho makua

The sum of the 1st nine terms of an arithmetic series is 216. The 1st,3rd and the 7th terms of series form the 1st three terms of a geometric series. Find the 1st term and the constant difference of the arithmetic series ?

1. Steve

just write what they told you:

9/2 (2a+8d) = 216
(a+2d)/(a) = (a+6d)/(a+2d)

Now solve for a and d.

Now, just for precision, you mean arithmetic sequence. A series is the sequence of partial sums of a sequence. For example,

sequence: 3,7,11,15,19,...
series: 3,10,21,36,55,...

2. Brittney

The third term of an arithmetic sequence is 14 and the ninth term is -1 find the first four term of the sequence

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