Which of the following is an even function?

If $f(x) = \log \left( \frac{1 + x}{1 - x} \right)$,then $f(x)$ is

Let $f(x) = \begin{cases} \frac{1}{2}, & \text{if } 0 \le x \le \frac{1}{2} \\ \frac{1}{3}, & \text{if } \frac{1}{2} < x \le 1 \end{cases}$,then $f$ is

For a real number $x$,let $[x]$ denote the greatest integer less than or equal to $x$,and let $\{x\} = x - [x]$. The number of solutions $x$ to the equation $[x]\{x\} = 5$ with $0 \leq x \leq 2015$ is

Let $f = \{(1, 1), (2, 3), (0, -1), (-1, -3)\}$ be a linear function from $\mathbb{Z}$ into $\mathbb{Z}$. Find $f(x)$.

The equation $6^{x}+8^{x}=10^{x}$ has