How can you do such things?
First put
$x$
and
$j$
in fixed locations
$X$
and
$Y$
.
Then set up the following columns on the spreadsheet:

$f({x}_{j})$
:

In the first column enter the successive values of
$f({x}_{j})$
starting with the first, known value.

For roots you can start with
${x}_{0}=f({x}_{0})=1$
.

Compute later values
$f({x}_{j})$
by using the linear approximation tangent line at
${x}_{j-1}$
evaluated at argument
$x,fL{x}_{j-1}(x)$
or
$f({x}_{j-1})+f\text{'}({x}_{j-1})(x-{x}_{j-1})$
. (
${x}_{j-1}$
is the entry in the second column in the previous row.)

${x}_{j}$
:

In the second column apply the inverse function,
${f}^{-1}$
to the value in the first column.

Once you have entered your instructions for
$f({x}_{1})$
and
${x}_{1}$
, you can copy these down a hundred rows, and you are done.