原式=(x²-2x+4)/(x+2)(x²-2x+4)-12/(x+2)(x²-2x+4)
=(x²-2x+4-12)/(x+2)(x²-2x+4)
=(x²-2x-8)/(x+2)(x²-2x+4)
=(x+2)(x-4)/(x+2)(x²-2x+4)
=(x-4)/(x²-2x+4)第一部不明白