Question

Find the 9th term of the sequence $1,-1,1,-\mathrm{1...}$

• A. $1$
• B. $-1$
• C. $2$
• D. $-2$

Answer 1

The correct option is A $1$

Given series is $1,-1,1,-1,....$

Here first term $=a=1$, common ratio $=-1$
We know the formula for $n^{th}$ term,
$t_n=a{r}^{n-1}$
$t_9=1\times -1^{9-1}$
$=1\times -1^8$
$=1\times 1$
$=1$