Question $1(8$ points$)$

Which of the following functions is a one$-$to$-$one function?

$f$:$ZZ,$ where $f(n)=|n|-1$

$f$:$RR,$ where $f(x)=4x^2$

$f$:$ZZ,$ where $f(n)=n^2+6$

$f$:$RR,$ where $f(x)=5x^3+3$