y=(x-1)/(x+2)²
y`=[(x+1)²-2(x-1)(x+1)]/(x+1)⁴
y`=(3-x)/(x+1)³
y``=[-(x+1)³-3(3-x)(x+1)²]/(x+1)^6=(2x-10)/(x+1)⁴