If x2 + y2 - 4x - 4y + 8 = 0, then the value of x - y is?

Answer: Option C

$$\begin{array}{rl}& x^2+y^2-4x-4y+8=0\\ & \Rightarrow x^2+4-4x+y^2+4-4y=0\\ & \Rightarrow {\left(x-2\right)}^2+{\left(y-2\right)}^2=0\\ & {\left(x-2\right)}^2=0\iff x=2\\ & {\left(y-2\right)}^2=0\iff y=2\\ & \therefore x-y\\ & \Rightarrow 2-2\\ & \Rightarrow 0\end{array}$$