Question 17Let $f(n)=\dfrac{x_1+x_2+\cdots+x_n}{n},$ where $n$ is a positive integer. If $x_k=(-1)^k,$ $k=1,$ $2,$ $\ldots,$ $n,$ the set of possible values of $f(n)$ is:$\{0\}$$\left\{\dfrac1n\right\}$$\left\{0,-\dfrac1n\right\}$$\left\{0,\dfrac1n\right\}$$\left\{1,\dfrac1n\right\}$