You make the polynomial into a square by dividing the second term by 2 and squaring it. 22 divided by 2 is 11. And 11 squared is 121. The completed square for the polynomial is then Z^2 + 22Z + 121. Thus C must equal 121 for the polynomial to be a square. This polynomial is the square of Z + 11 or (z + 11)^2.