Question

What is the recursive rule for the sequence 2, -1, 1/2 , -1/4

Answer 1

Answer:

$a_n=\frac{-1}{2}a_{n-1}$

$a_1=2$

Step-by-step explanation:

The recursive rule is a term defined in terms of other terms in the sequence.

The is a geometric sequence because it has a common ratio.

The common ratio can be found by dividing a term by previous term.

For example, all of these are equal:

$\frac{-1}{2}$

$\frac{\frac{1}{2}}{-1}$

$\frac{\frac{-1}{4}}{\frac{1}{2}}$

They are all equal to $\frac{-1}{2}$.

So we are saying:

$\frac{\text{term}}{\text{previous term}}}=\frac{-1}{2}$

More formally:

$\frac{a_n}{a_{n-1}}=\frac{-1}{2}$.

Multiply both sides by $a_{n-1}$:

$a_n=\frac{-1}{2}a_{n-1}$

When doing recursive form, you need to state a term of the sequence (or more depending on the recursive form you have).

So the first term is 2.

So the full thing for the answer is:

$a_n=\frac{-1}{2}a_{n-1}$

$a_1=2$