format long

n=4;
x = [0.6 0.7 0.8 0.9];
f = [cos(0.6) cos(0.7) cos(0.8) cos(0.9)];
L = ones(1,n);
a = 0.739141
for i =1:n
  for j=1:n
    if(i!=j)        
      L(i) = L(i) * (a-x(j))/(x(i)-x(j));
    end
  end
end
s=0
for i=1:n
  s = s + f(i)*L(i);
end
s