while(abs(x1-x2)>epsilon){
        std::cout.setf(std::ios::fixed, std::ios::floatfield );
        std::cout.precision(20);
        y1=x1*(x1*x1-1)*sin(x1)*sin(x1);
        y2=x2*(x2*x2-1)*sin(x2)*sin(x2);
        x0=x1-(y1*(x1-x2)/(y1-y2));
        x2=x1;
        x1=x0;
        y0=(x0*x0*x0-x0)*sin(x0)*sin(x0);
        y2=y1;
        y1=y0;
        j++;
    }