function [ ] = chmethodslagranga (a,b,n)
syms x;
%F(x)=3*x-cos(x)-1;
ezplot('3*x-cos(x)-1'),hold on
axis([0 5 -0.1 0.1])
xx=linspace(a,b,n+1);
yy=zeros(1,n+1);
res=0;
x1=xx(1);
x2=xx(1);
for i=1:n+1
  yy(i)=3*xx(i)-cos(xx(i))-1;
end
y1=lagrange (xx,yy,n,xx(1));
y2=y1;
for l=1:n+1
   res=lagrange(xx,yy,n,xx(l));
  s=3*xx(l)-cos(xx(l))-1;
  x2=xx(l);
  y2=res;
  % рисую график полинома
  plot([x1,x2],[y1,y2],'g');
  disp([s res s-res xx(l)]);
  x1=x2;
  y1=y2;
end
ry1=3*1-cos(1)-1-lagrange(xx,yy,n,1);
ry2=ry1;
rx1=1;
rx2=1;
for i=1:0.001:10
   res=lagrange(xx,yy,n,i);
   s=3*i-cos(i)-1;
   rx2=i;
   ry2=s-res;
   if ry1~=ry2
   % рисую график разницы
   plot([rx1,rx2],[ry1,ry2],'r');
   rx1=rx2;
   ry1=ry2;
   end
end
end

function [res] =lagrange (xx,yy,n,t)
res=0;
for i=1:n+1
  pn=1;
  for j=1:n+1
      if i~=j
          pn=pn*(t-xx(j))/(xx(i)-xx(j));
      end
  end
  res=res+pn*yy(i);
end
end