Question

What is the 20th term of the linear sequence 15,7,-1?

Answer 1

`-137`

Explanation:

We have a sequence with the first term being 15 and each subsequent term is the value of the one before, minus 8:

`x_n=15-8(n-1)`

This shows that for `n=1, x=15`, which is right because 15 is our first term.

For `n=3, x=15-8(2)=-1`, which also checks.

And so for the 20th term:

`n=20=>x_20=15-8(20-1)=15-152=-137`