Hi, I am having a little trouble finding the roots of Bessel's function J0 between -4 and 4 using the newton Raphson method, the main issue I am having is not knowing what to input at a certain point.

f:=x->x-evalf(cos(x));
                     f := x -> x - evalf(cos(x))

> low:=-10;

                              low := -10

> up:=10;

                               up := 10

> step:=1;

                              step := 1