format long 
x = 0.6;
f = @(x)  cos(0.6);
while (abs(f(x)-x) >= 10^(-10))
  x = f(x);
  end
  L(1:4) = 1;
  X = [0.6 0.7 0.8 0.9];
  ans = 0;
  for(i = 1 : 4)
    for(j = 1 : 4)
      if(i != j)
        L(i) = L(i) * (x-X(j))/(X(i)-X(j));
       end
     end
     ans = ans + L(i)*f(X(i));
   end
   x 
   ans