$2\mathrm{.}1\mathrm{.}3$ Define $f$:$R^2{R}^{2}by$

$f(x,y,)=(x,y+h(x))$

for some continuously differentiable function $hof$ one variable.

$2\mathrm{.}1\mathrm{.}3\mathrm{.}1$ Show that $fis$ one$-to-$one