What is the 20th term of the arithmetic sequence 2, –4, –10, … ?
the nth term of an AP
here we have
and it is seen that
If the sequence is denoted by the series
so that the first term is
The terms in the sequence
You can keep writing the terms until you get to the 20th, but that is not a very mathematical way of doing it and would be VERY time-consuming if you were asked for the 200th term for example.
Find the rule for the sequence... called
If the difference is
You need to adjust the rule to start at the correct number,
But the first term must be
Now find the 20th term: