A sequence is defined as follows

[Dleonb]

Hi,

I hope that you might be able to help me. I am busy working through the entire MGMAT series and am on book 3 (4th edition). Everything has been really great until now, but I am really struggling to understand one of your answers to question 5 from the problem set for Chapter 11.

Question is as follows:
"A Sequence is defined as follows: a(subscript)1 = 1, and a(subscript)n=na(subscript)n-1 for all integer n≥2. Write an explicit formula for an in terms of n.

I would really appreciate it if someone could, "show" me how you got a value for "n"?

I hope to hear from an instructor soon.

Thanks in advance,

D'leon

[tim]

this is not about getting "a value for 'n'". n can take on any value. this is the point of sequences. it sounds like you may want to review what sequences are in the first place, and then if you have further questions we'll be glad to help you out..

[Dleonb]

Hi Tim,

It seems that I'm struggling to communicate correctly. I have gone through both, Part 1 and Part 2, on sequences, and I am relatively comfortable with all of it. There is only ONE question I did not get right, and I could not follow your logic in the answers section because I could not understand how you got "n". In the answers, all it says is:
a1 = 1
a2 = 1 x 2 = 2
a3 = (1 x 2) x 3 = 6
a4 = (1 x 2 x 3) x 4 = 24

and therefore it is the same as n! (I understand how it is the same as n factorial), I am just not clear on the above. Please try explain it to me?

[tim]

i suppose i am struggling to understand you. please note that asking a question such as "how you got 'n'" when n is the index of the sequence indicates a fundamental lack of understanding of what sequences are. before we can help you with this one, you are going to need to do a thorough review of what sequences are or you are going to need to thoroughly rework your question into something that makes sense..

[saeed.rh]

thanks tim

i also do have a question here:

how can i use direct formula S = x (k)n to reach to the answer (n!)?

[jnelson0612]

thanks tim

i also do have a question here:

how can i use direct formula S = x (k)n to reach to the answer (n!)?

Hi saeed,
You want to be careful here. The direct formula can be used if there is an equal spacing between the terms in a sequence. For example, 2, 4, 6, 8, 10 or 5, 10, 15, 20 would be equally spaced.

In this case, the spacing between terms is not equal. The terms are 1, 2, 6, 24, and so on. Thus, we could not use the direct formula for this particular sequence.