[(x-1)(x-2)*√(x+1)]/(x³+1)=[(x-1)(x-2)*√(x+1)]/[(x+1)(x²-x+1)]=[(x-1)(x-2)]/[(x²-x+1)*√(x+1)]要使极限为∞，那么分子≠0，分母=0∴(x²-x+1)*√(x+1)=0，∴x=-1
