Homework Help: Arithmetic Sequence

Posted by Nina on Sunday, September 30, 2012 at 5:31am.

Given the third term of an arithmetic sequence less than the fourth term by three. The seventh term is two times the fifth term. Find the common difference and the first term.

Arithmetic Sequence - Steve, Sunday, September 30, 2012 at 7:47am
since the terms have a constant difference, the difference is 3.

a+6*3 = 2(a+4*3)
a+18 = 2a+24
a = -6

sequence is -6,-3,0,3,6,9,12,15,18,21,24
T7 = 12 = 2*6 = 2T5

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