[tom2020]

Hi

My question is about sequence and series.

I am bit confused how to work these out:

Consider the sequences below:

Un=-1.8, Un+0.7 (n=1,2,3... )
I need to find the first four term of the sequences and closed form of the sequences;
use the closed form to find the value of N when Un=45.1

I asumed it is arithematic sequences; please correct me if am wrong;

[rwinterton]

Un=-1.8, Un+0.7 (n=1,2,3... )

I'm not sure you have shown us a sequence. Usually you need at least three elements of the sequence to determine a pattern.

Does U1=-1.8 and U2 = +0.7. You can get from 1 to 2 by adding 2.5, but you can also get from 1 to 2 by multiplying by -0.7/1.8 so with only two elements of the sequence, you can't tell what operations must be performed and you can't tell the type of sequence.

Basically, you need to look carefully at the values and figure out what mathematical operations are required to get from the first to the second to the third number in the sequence.