Find the sixteenth term of the arithmetic progression -91; -89.

In our case, a1 = – 91, a2 = – 89.
Since in the arithmetic progression each term (starting from the second) is equal to the sum of the previous and the same number d (difference), we can find the difference:
d = an – a (n-1),
d = a2 – a1;
d = – 89 – (- 91);
d = 2;
Let’s use the formula to find the nth term of the arithmetic progression:
an = a1 + d (n – 1);
a16 = a1 + d (16 – 1);
a16 = – 91+ 2 * 15;
a16 = – 91+ 30;
a16 = – 61.
Answer: a16 = – 61.