clc;
x = -3:10;
a = 0;
b = 7;
f = 'x.^2 + 5*x - 20';
figure(1); clf; hold on;
plot (x, eval(f));
x = a;
fa = eval(f);
x = b;
fb = eval(f);
if (fa*fb > 0)
break;
end;
z = zeros(1,2);
for (i = 1:10)
c = (b + a) /2;
x = c;
z = [z; c, fc];
fc = eval(f);
z = [z; c, fc];
plot(c, eval(f),'r.','markersize' ,6);
if (fb*fc > 0)
b = c;
fb=fc;
else
a = c;
fa=fc;
end;
end;