17. Given the function $f(x)=\log _{4}\left(4^{x}+1\right)+k x(k \in \mathbf{R})$ is an even function.
(1) Find the value of $k$;
(2) If the equation $f(x)=\log _{4}\left(\frac{m}{2^{x}}-1\right)$ has a solution, find the range of real number $m$.
(1) $f(x)=\log _{4}\left(4^{x}+1\right)+\log _{4} 4^{k x}=\log _{4}\left(4^{(k+1) x}+4^{k x}\right)$, so $(k+1) x=-k x \Rightarrow k=-\frac{1}{2}$.
(2) From (1), we know $f(x)=\log _{4}\left(2^{x}+2^{-x}\right) \Rightarrow 2^{x}+2^{-x}=\frac{m}{2^{x}}-1 \Rightarrow m=2^{2 x}+2^{x}+1=\left(2^{x}+\frac{1}{2}\right)^{2}+\frac{3}{4}>1$, so the range of real number $m$ is $(1,+\infty)$.