I need help with a code for a crank slider system with newtons Rhapson method.

Hi, i need to make a code in matlab of a crank slider system with the Newtons Rhapson. This is my code right now but because is a crank slider system D. how do i found D?

% Crank-slider solucionado por el metodo de Newton Rhapson 
clc;
clear;
%links 
a=1.4;
b=4; 
c=1;
%Angulos
th2=45;
th1=0;
th4=90;
%Primer valor de 'd' y 'theta3' para que entre al loop for end 
d=3;
th3=178;
error=0.001;

for i=1:100
    f1=a*cosd(th2)-d*cosd(th1)-b*cosd(th3)-c*cosd(th4);
    f2=a*sind(th2)-d*sind(th1)-b*sind(th3)-c*sind(th4);
    df1_th3=b*sind(th3);df1_d=d*sind(th1);
    df2_th3=-b*cosd(th3);df2_d=-d*cosd(th1);
    A=[df1_th3,df1_d;df2_th3,df2_d];
    x=inv(A)*-[f1;f2];
    if abs(sum(x))<=error
        iteration=i;
        break
    end
 
    th3=th3+x(1);
    d=d+x(2);
end
iteration=i;
disp(th3)
disp(d)