Question

已知集合I=R,A={x|x^2>4},B={x|(x+3)∕(x+1)≥2x/(x+1)},求(CRA)∩(CRB).

Answer 1

解…A＝﹛x|x²＞4﹜={x|x>2或x<-2},CRA={x|-2<=x<=2};(x 3)∕(x 4)≥2x／﹙x＋1),化为[-(x 3)(x 1) 2x(x 4)]/[(x 4)(x 1)]<=0,即（x 2 √7）（x 2-√7）/[（x 4)(x 1)]<=0,∴-2-√7<=x<-4,或-1<x<=√7-2，CRB={x|x<-2-√7，或-4<=x<=-1,或x>√7-2}，∴﹙CRA﹚∩﹙CRB﹚={x|-2<=x<=-1,或√7-2<x<=2}.

追问

B={x|(x+3)∕(x+1)≥2x/(x+1)},而不是B={x|(x+3)∕(x+4)≥2x/(x+1)},