分子有理化得
lim(x→－2) [（5＋X）－ 3]/[(X平方＋X－2)*(根号（5＋X）+ 根号3)]
= lim(x→－2) [(2＋X)/(X平方＋X－2)] / lim(x→－2) [根号（5＋X）+ 根号3)]
= lim(x→－2) (2＋X)/[(X+2)(X-1)] / (2根号3)
= lim(x→－2) 1/(X-1) / (2根号3)
= (-1/3) / (2根号3)
= - 根号3 /18