For this case we have the following polynomial: x ^ 2 + 6x The missing value to complete the square is given by: x ^ 2 + 6x + (6/2) ^ 2 Rewriting we have: x ^ 2 + 6x + (3) ^ 2 x ^ 2 + 6x + 9 Then, completing the square we have: (x + 3) ^ 2 Answer: the missing constant term in the perfect square is: 9