How can i find points intersecting x-axis on graph and show them on figure

m1=input('Enter value of mass 1=');
m2=input('Enter value of mass 2='); 
k1=input('Enter value of stiffness 1='); 
k2=input('Enter value of stiffness 2='); 
k3=input('Enter value of stiffness 3='); 
for i=1:3501 
   w(i)=2*(i-1); 
   x1(i)=1; 
   x2(i)=(x1(i)-((w(i)^2*m1*x1(i))/k2)); 
   x3(i)=(x2(i)-(w(i)^2*(m1*x1(i)+m2*x2(i))/k3));
end

plot(w,x3); 
xL = xlim;
yL = ylim;
line([0 0], yL); %x-axis
line(xL, [0 0]); %y-axis
axis([0,80,-10,10]); %set limit
xlabel('w');
ylabel('x');

Answer 1

[dpb]

Either

doc find    % nearest point (note to look for crossing, not zero) or
doc interp1 % interpolated location if not exact