Suppose That $f(x)$ Is a Power Function and That $f(9)=\frac{1}{9}$ Must $f(x)=\frac{1}{x}$

True/False

Suppose that $f(x)$ is a power function and that $f(9)=\frac{1}{9}$ . Must $f(x)=\frac{1}{x}$ ?