Newton Raphson method of finding multiple roots

I'm trying to find multiple roots of an equation using the newton raphson method (must be newton raphson). I have code which can find one root, however for my specific parameters there are 12 roots to find. (Pos/neg of 6 values.) I need to have all of the roots, not just the first one my code finds.

here is my code, thanks

clear; clc; close;

% guess value for root

x = input('Enter a seed value for x: ')

% Get acceptable Error

err = 0.01

% formula coefficients used

L = 0.8

Bi = 0.5

ferr = 100; % initializing acceptable error for while loop

Fold = 100; % initializing old F value for while loop

f1 = (x*L)/(Bi); % function 1

f2 = cot(x*L); % function 2

f = f1-f2; % difference between functions

f1p = (L/Bi); % Derivative of function 1

f2p = -L*csc(L*x)^2; % derivative of function 2

fp = f1p-f2p; 

while abs(f) > err   % difference of the functions is greater than error

     f = (x*L/Bi)- cot(x*L); % function again so it re-evaluates inside loop

     fp = (L/Bi) + L*csc(L*x)^2; % derivative again so it re-evaluates inside loop

     Fold = f; % update old F value for newtons formula use

     x = x - f/fp % update x value to get closer to real root

     ferr = f - Fold; % update function error (not really useful here)

     pause(1)

end

x1 = -3.5*pi:.1:3.5*pi;

f1 = (x1*L)/(Bi); % function 1

f2 = cot(x1*L); % function 2

plot(x1,f1,'color','r');

hold on;

plot(x1,f2,'color','b');