Find the 5th Term 1/2 , -1/4 , 1/8 , -1/16

$\frac{1}{2}$ , $- \frac{1}{4}$ , $\frac{1}{8}$ , $- \frac{1}{16}$

Step 1

This is a geometric sequence since there is a common ratio between each term. In this case, multiplying the previous term in the sequence by $- \frac{1}{2}$ gives the next term. In other words, $a_{n} = a_{1} r^{n - 1}$ .

Geometric Sequence: $r = - \frac{1}{2}$

Step 2

This is the form of a geometric sequence.

$a_{n} = a_{1} r^{n - 1}$

Step 3

Substitute in the values of $a_{1} = \frac{1}{2}$ and $r = - \frac{1}{2}$ .

$a_{n} = \frac{1}{2} {(- \frac{1}{2})}^{n - 1}$

Step 4

Use the power rule ${(a b)}^{n} = a^{n} b^{n}$ to distribute the exponent.

Apply the product rule to $- \frac{1}{2}$ .

$a_{n} = \frac{1}{2} ({(- 1)}^{n - 1} {(\frac{1}{2})}^{n - 1})$

Apply the product rule to $\frac{1}{2}$ .

$a_{n} = \frac{1}{2} ({(- 1)}^{n - 1} \frac{1^{n - 1}}{2^{n - 1}})$

Step 5

One to any power is one.

$a_{n} = \frac{1}{2} ({(- 1)}^{n - 1} \frac{1}{2^{n - 1}})$

Step 6

Combine ${(- 1)}^{n - 1}$ and $\frac{1}{2^{n - 1}}$ .

$a_{n} = \frac{1}{2} \cdot \frac{{(- 1)}^{n - 1}}{2^{n - 1}}$

Step 7

Combine.

$a_{n} = \frac{1 {(- 1)}^{n - 1}}{2 \cdot 2^{n - 1}}$

Step 8

Multiply $2$ by $2^{n - 1}$ by adding the exponents.

Multiply $2$ by $2^{n - 1}$ .

Raise $2$ to the power of $1$ .

$a_{n} = \frac{1 {(- 1)}^{n - 1}}{2^{1} \cdot 2^{n - 1}}$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$a_{n} = \frac{1 {(- 1)}^{n - 1}}{2^{1 + n - 1}}$

Combine the opposite terms in $1 + n - 1$ .

Subtract $1$ from $1$ .

$a_{n} = \frac{1 {(- 1)}^{n - 1}}{2^{n + 0}}$

Add $n$ and $0$ .

$a_{n} = \frac{1 {(- 1)}^{n - 1}}{2^{n}}$

Step 9

Multiply ${(- 1)}^{n - 1}$ by $1$ .

$a_{n} = \frac{{(- 1)}^{n - 1}}{2^{n}}$

Step 10

Substitute in the value of $n$ to find the $n$ th term.

$a_{5} = \frac{{(- 1)}^{(5) - 1}}{2^{5}}$

Step 11

Simplify the numerator.

Subtract $1$ from $5$ .

$a_{5} = \frac{{(- 1)}^{4}}{2^{5}}$

Raise $- 1$ to the power of $4$ .

$a_{5} = \frac{1}{2^{5}}$

Step 12

Raise $2$ to the power of $5$ .

$a_{5} = \frac{1}{32}$

Find the 5th Term 1/2 , -1/4 , 1/8 , -1/16

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