clear, clc, close all;
x=[1,3,4,5]';
y=[3,3,0,11]';

A=ones(size(x));

for i=2:length(x)
   A=[A A(:,end).*(x-x(i))] ;
end
c=A\y;
p7=c(1)
addera=1
for i=2:length(x)
    addera=addera*(7-x(i));
    p7=p7+c(i)*addera;
end
p7
c=polyfit(x,y,3);
p7=polyval(c,7)