Ok, someone please tell me I'm not crazy, here.
We have a sequence, first five terms are -2, 1, 4, 7, 10. We are directed to find an explicit rule A-sub-n =
DS put A-sub-n = 3(n-1)-2, which appears to work just fine. We are also directed to find the 100th term, which comes out to 295. A-sub-100 = 3(99)-2 which equals 295. This was graded as correct.
The teacher took off one point on the question, with the comment not to forget the A-sub-n-minus-1 in the equation, and "don't we want to subtract 5?" So she wants it to be A-sub-n = 3(A-sub-n-minus-1) -5.
Am I not correct in thinking that this would require us to actually go through 100 of these terms to find out what the 99th term was, before getting to the 100th one? And it wouldn't come up with 295, either. A-sub-2 = 3(-2)-5 would equal -11, not 1. Unless I'm crazy.
A-sub-n-minus-1 is used for recursive formulas, right? An explicit formula works off the term number, not the actual term? And in a recursive formula, you first define the first term, and then work the formula off of that, where each A-sub-n-minus-1 means the previous term, not the term numbers. The question doesn't seem to be phrased as asking for a recursive formula, either in the statement (find an explicit formula) or in the part you fill in, which includes A-sub-n= and then the line for filling in the blank. And they can't possibly want us (or him, lol) to work out 100 of these to get the answer.
Help?
Last edited by Nautigal; 09/10/15 08:52 PM.
