限时集训(九)指数与指数函数(限时:45分钟满分:81分)一、选择题(本大题共6小题,每小题5分,共30分)1.化简的结果是()A.-B.C.-D.2.(·天津高考)已知a=212,b=-0.5,c=2log52,则a,b,c的大小关系为()A.c0时,f(x)的单调性;(3)若3tf(2t)+mf(t)≥0对于t∈恒成立,求m的取值范围.答案限时集训(九)指数与指数函数1.A2.A3.C4.C5.B6.B7.(1,5)8.9.110.解:(1)[f(x)]2-[g(x)]2=(ex-e-x)2-(ex+e-x)2=(e2x-2+e-2x)-(e2x+2+e-2x)=-4.(2)f(x)f(y)=(ex-e-x)(ey-e-y)=ex+y+e-x-y-ex-y-e-x+y=[ex+y+e-(x+y)]-[ex-y+e-(x-y)]=g(x+y)-g(x-y),∴g(x+y)-g(x-y)=4.①同理,由g(x)g(y)=8,可得g(x+y)+g(x-y)=8.②由①②解得g(x+y)=6,g(x-y)=2,∴=3.11.解:y=lg(3-4x+x2),∴3-4x+x2>0,解得x<1或x>3.∴M={x|x<1,或x>3}.f(x)=2x+2-3×4x=4×2x-3×(2x)2.令2x=t,∵x<1或x>3,∴t>8或08或08时,f(t)∈(-∞,-160),∴当2x=t=,即x=log2时,f(x)max=.综上可知,当x=log2时,f(x)取到最大值为,无最小值.12.解:(1)当x≤0时,f(x)=3x-3x=0,∴f(x)=2无解.当x>0时,f(x)=3x-,令3x-=2.∴(3x)2-2·3x-1=0,解得3x=1±.∵3x>0,∴3x=1+.∴x=log3(1+).(2)∵y=3x在(0,+∞)上单调递增,y=在(0,+∞)上单调递减,∴f(x)=3x-在(0,+∞)上单调递增.(3)∵t∈,∴f(t)=3t->0.∴3tf(2t)+mf(t)≥0化为3t+m≥0,即3t+m≥0,即m≥-32t-1.令g(t)=-32t-1,则g(t)在上递减,∴g(x)max=-4.∴所求实数m的取值范围是[-4,+∞).