4.若a>1,b<1,则下列结论中正确的是( )
A.1/a>1/b B.b/a>1
C.a2>b2 D.ab 解析由a>1,b<1得a-1>0,b-1<0,所以(a-1)(b-1)<0,展开整理,得ab 答案D 5.已知1≤a+b≤5,-1≤a-b≤3,则3a-2b的取值范围是( ) A.[-6,14] B.[-2,14] C.[-6,10] D.[-2,10] 解析令3a-2b=m(a+b)+n(a-b), 则{■(m+n=3"," @m"-" n="-" 2"," )┤所以{■(m=1/2 "," @n=5/2 "." )┤ 因为1≤a+b≤5,-1≤a-b≤3, 所以1/2≤1/2(a+b)≤5/2,-5/2≤5/2(a-b)≤15/2, 故-2≤3a-2b≤10. 答案D 6.已知0 解析∵a-1/a=("(" a+1")(" a"-" 1")" )/a<0,∴a<1/a. 又a-a2=a(1-a)>0,∴a>a2.∴a2 答案a2 7.已知-3 解析由题意可知0 答案(0,8) 8.设a>b>c>0,若x=√(a^2+"(" b+c")" ^2 ),y=√(b^2+"(" c+a")" ^2 ),z=√(c^2+"(" a+b")" ^2 ),则x,y,z之间的大小关系是 .(从小到大)