Question

Indicate the general rule for the arithmetic sequence with a3 = -12 and a8 = -37

Answer 1

Answer:

The general rule is $a_n = -2 - 5(n-1)$

Step-by-step explanation:

Arithmetic sequence:

In an arithmetic sequence, the difference between consecutive terms is always the same, and this difference is called common difference.

The general rule of an arithmetic sequence is given by:

$a_{n} = a_1 + (n-1)d$

In which $a_1$ is the first term and d is the common difference.

We can also find the nth term as a function of a term m, using:

$a_n = a_m + (n-m)d$

a3 = -12 and a8 = -37

First we find the common difference. So

$a_n = a_m + (n-m)d$

$a_8 = a_3 + (8-3)d$

$-37 = -12 + 5d$

$5d = -25$

$d = -\frac{25}{5}$

$d = -5$

So

$a_n = a_1 - 5(n-1)$

Finding the first term:

$a_n = a_1 - 5(n-1)$

Since $a_3 = -12$

$a_n = a_1 - 5(n-1)$

$a_3 = a_1 - 5(3-1)$

$a_1 = a_3 + 10 = -12 + 10 = -2$

So the general rule is:

$a_n = a_1 - 5(n-1)$

$a_n = -2 - 5(n-1)$