I have the following sequence {n^4-6n^2}. I have to determine if the sequence is non-decreasing, increasing or decreasing.

Payton Rasmussen

Payton Rasmussen

Answered question

2022-10-07

Non-decreasing sequences
I have the following sequence
{ n 4 6 n 2 }
I have to determine if the sequence is non-decreasing, increasing or decreasing.
In my opinion, the sequence is neither, decreasing, non-decreasing nor increasing because it seems to be increasing for all the terms except for the first and second term. Am I right or I am right?
By the way,is there category for such a sequence? where you have an interval of increasing terms and one of decreasing terms or is such a sequence not even possible?

Answer & Explanation

bequejatz8d

bequejatz8d

Beginner2022-10-08Added 6 answers

Step 1
The polynomial factorises as n 2 ( n 2 6 ) ,, which vanishes somewhere between n = 2 and n = 3 if we for the moment think of n as a real variable. It then increases afterwards. Thus, you're right that it cannot be monotonic.
Step 2
Sequences that are not monotonic may generally be classified as oscillating.
hifadhinitz

hifadhinitz

Beginner2022-10-09Added 2 answers

Step 1
Let a n = n 4 6 n 2
Step 2
then a n + 1 a n = ( n + 1 ) 4 6 ( n + 1 ) 2 ( n 4 6 n 2 ) =

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