function [k, approximate_error] = bisection()
cn=[1,-1,-2];
a = 1.5;
b = 5;
x0 = (a+b)/2;
k = 0;

    while(x0~= 2)
        if(polyval(cn,x0)*polyval(cn,a)<0)
            x0 = (a+x0)/2;
        end
            if(polyval(cn,x0)*polyval(cn,b)<0)
                x0=(b+x0)/2;
            end
         k = k + 1,
         approximate_error(k) = abs(x0 - 2) /2,
    end
    x0,

    x = -1.5:0.01:5;
    y = polyval(cn,x);
    figure(1)

    plot(x,y)
    grid on;
    hold on;