For each of the following functions, state whether they are one-to-one or not. (You must enter T or F -- True and False will not work.)

 1. $f: [-12,\infty) \longrightarrow \textbf{R}, f(x)={1 \over {x^2+1}}$
 2. $f: [5,\infty) \longrightarrow \textbf{R}, f(x)={1 \over {x^2+1}}$
 3. $f: \textbf{R}-\{0\} \longrightarrow \textbf{R}, f(x)=1/x^3$
 4. $f: \textbf{R}-\{0\} \longrightarrow \textbf{R}, f(x)=1/x^2$
 5. $f: [5,\infty) \longrightarrow \textbf{R}, f(x)=x^2$