Get rid of the calls to set and just do this:
handles.ans1 = (-(handles.mydata.b) + dis) /(2*(handles.mydata.a));
handles.ans2 = (-(handles.mydata.b) - dis) /(2*(handles.mydata.a))
In the second callback do this instead:
x=0:(length(handles.ans1) - 1);
plot(x,handles.ans1, handles.axes1);
grid on;
hold on;
x=0:(length(handles.ans2) - 1);
plot(x,handles.ans2, handles.axes2);
If it still doesn't work, then find a call to guidata() somewhere in your code and copy it to the last line of the callback that assigns handles.ans1 and handles.ans2.
