If the second difference column is constant then the function is a quadratic.
Use the first three numbers to solve for
Okay, first post in the forums for me
This is my first year in high school geometry (i'm a freshman) and I'm loving it! I've run into a spot of trouble though...
My geometry teacher challenged us with a problem, and if I get it right, he will give me an A for the semester. I don't have the exact conjecture written down, but basically it is a formula to find the nth term in a sequence. For example, this formula could tell you what the 65th term in the sequence 4, 7, 13, 21.... (1st difference is 3, 6, 9, 2nd difference is 3,3,3). I have yet to learn proofs, which is why this is a challenge.
From the research I have done, I figure that mathematical induction would be the best method. I am guessing that if I can prove it works for a difference of 1, I can prove it for 2,3,4,5, etc. Am I correct in my thinking? Is there a better method? Also, any advice in the process; this is my first time proving a theorem (and he said it IS a theorem, as he has already proven it). Thanks in advance!
I'll edit this tomorrow when I write down the formula, sorry about its absence right now. If any more information is needed, just ask. I look forward to helping out in the algebra section, and spending some time on these forums!
Okay, Here is all of the information, with a better explanation of what I need help on.
The theorem is used to solve for the nth term in an arithmetic sequence. The variables are as such:
the number term you are looking for (e.g. the 54th term or the 78th term)
the number of terms shown (e.g in the sequence of 2,4,6,8... this value would be 4)
the 1st difference
the last term shown (e.g. 8 in the above example)
A quick example in case I did not explain it thoroughly:
Given the sequence 3,6,9,12,15,18,21... determine the 86th term.
The 86th term is therefore 258. I understand all of the above. The challenge is to prove this as a theorem, and that is what I am confused about, as I have not yet learned proofs. It is my understanding that if I can prove it to be true when , I can then prove it to be true for . I don't quite understand how to do that, but I can figure it out with time. What I don't get is how to prove this for negative integers. Can anybody offer an explanation at this point? Thanks.
Your general idea about induction is correct. So, you prove the formula is correct for k = 1. Then you prove, under the assumption the formula for is correct, that the formula for is correct. One addition: you may have to do this for variables other than k. (Or maybe not. You should do something to deserve your A, don't you think?)