If x2 + y2 – 4x – 4y + 8 = 0, then the value of x

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x² + y² – 4x – 4y + 8 = 0
⇒ x² – 4x + 4 + y² – 4y + 4 = 0
⇒ (x – 2)² + (y – 2)² = 0
⇒ x = 2 and y = 2
∴ x – y = 2 – 2 = 0