function plotnewtoninterp(x,y,c,varargin)
%plot 50 points
n=length(x);
X=linspace(min(x),max(x),100);
Y=c(n);
for j=n-1:-1:1
  Y = Y.*(X-x(j)) + c(j);
end

plot(x,y,'bo');hold on;
if nargin>=4
  plot(X,Y,varargin{:});
else
  plot(X,Y,'k-');
end