y²-2y = x
y²-2y+1 = x+1
(y-1)² = x+1
y = ±√(x+1) + 1
= √(x+1) + 1 或 -√(x+1) + 1
y' = 1/[2√(x+1)] 或 y' = -1/[2√(x+1)]
∴y' = ±1/[2√(x+1)]