1.下列命題中,真命題是( )A.函數(shù)y=1x是奇函數(shù),且在定義域內(nèi)為減函數(shù)B.函數(shù)y=x3(x-1)0是奇函數(shù),且在定義域內(nèi)為增函數(shù)C.函數(shù)y=x2是偶函數(shù),且在(-3,0)上為減函數(shù)D.函數(shù)y=ax2+c(ac≠0)是偶函數(shù),且在(0,2)上為增函數(shù)解析:選C.選項(xiàng)A中,y=1x在定義域內(nèi)不具有單調(diào)性;B中,函數(shù)的定義域不關(guān)于原點(diǎn)對(duì)稱;D中,當(dāng)a<0時(shí),y=ax2+c(ac≠0)在(0,2)上為減函數(shù),故選C.2.奇函數(shù)f(x)在區(qū)間[3,7]上是增函數(shù),在區(qū)間[3,6]上的最大值為8,最小值為-1,則2f(-6)+f(-3)的值為( )A.10 B.-10C.-15 D.15解析:選C.f(x)在[3,6]上為增函數(shù),f(x)ax=f(6)=8,f(x)in=f(3)=-1.∴2f(-6)+f(-3)=-2f(6)-f(3)=-2×8+1=-15.3.f(x)=x3+1x的圖象關(guān)于( )A.原點(diǎn)對(duì)稱 B.y軸對(duì)稱C.y=x對(duì)稱 D.y=-x對(duì)稱解析:選A.x≠0,f(-x)=(-x)3+1-x=-f(x),f(x)為奇函數(shù),關(guān)于原點(diǎn)對(duì)稱.4.如果定義在區(qū)間[3-a,5]上的函數(shù)f(x)為奇函數(shù),那么a=________.解析:∵f(x)是[3-a,5]上的奇函數(shù),∴區(qū)間[3-a,5]關(guān)于原點(diǎn)對(duì)稱,∴3-a=-5,a=8.答案:81.函數(shù)f(x)=x的奇偶性為( )A.奇函數(shù) B.偶函數(shù)C.既是奇函數(shù)又是偶函數(shù) D.非奇非偶函數(shù)解析:選D.定義域?yàn)閧xx≥0},不關(guān)于原點(diǎn)對(duì)稱.2.下列函數(shù)為偶函數(shù)的是( )A.f(x)=x+x B.f(x)=x2+1xC.f(x)=x2+x D.f(x)=xx2解析:選D.只有D符合偶函數(shù)定義.3.設(shè)f(x)是R上的任意函數(shù),則下列敘述正確的是( )A.f(x)f(-x)是奇函數(shù)B.f(x)f(-x)是奇函數(shù)C.f(x)-f(-x)是偶函數(shù)D.f(x)+f(-x)是偶函數(shù)解析:選D.設(shè)F(x)=f(x)f(-x)則F(-x)=F(x)為偶函數(shù).設(shè)G(x)=f(x)f(-x),則G(-x)=f(-x)f(x).∴G(x)與G(-x)關(guān)系不定.設(shè)(x)=f(x)-f(-x),∴(-x)=f(-x)-f(x)=-(x)為奇函數(shù).設(shè)N(x)=f(x)+f(-x),則N(-x)=f(-x)+f(x).N(x)為偶函數(shù).4.已知函數(shù)f(x)=ax2+bx+c(a≠0)是偶函數(shù),那么g(x)=ax3+bx2+cx( )A.是奇函數(shù)B.是偶函數(shù)C.既是奇函數(shù)又是偶函數(shù)D.是非奇非偶函數(shù)解析:選A.g(x)=x(ax2+bx+c)=xf(x),g(-x)=-x•f(-x)=-x•f(x)=-g(x),所以g(x)=ax3+bx2+cx是奇函數(shù);因?yàn)間(x)-g(-x)=2ax3+2cx不恒等于0,所以g(-x)=g(x)不恒成立.故g(x)不是偶函數(shù).5.奇函數(shù)y=f(x)(x∈R)的圖象必過(guò)點(diǎn)( )A.(a,f(-a)) B.(-a,f(a))C.(-a,-f(a)) D.(a,f(1a))解析:選C.∵f(x)是奇函數(shù),∴f(-a)=-f(a),即自變量。璦時(shí),函數(shù)值為-f(a), 故圖象必過(guò)點(diǎn)(-a,-f(a)).6.f(x)為偶函數(shù),且當(dāng)x≥0時(shí),f(x)≥2,則當(dāng)x≤0時(shí)( )A.f(x)≤2 B.f(x)≥2C.f(x)≤-2 D.f(x)∈R解析:選B.可畫f(x)的大致圖象易知當(dāng)x≤0時(shí),有f(x)≥2.故選B.7.若函數(shù)f(x)=(x+1)(x-a)為偶函數(shù),則a=________.解析:f(x)=x2+(1-a)x-a為偶函數(shù),∴1-a=0,a=1.答案:18.下列四個(gè)結(jié)論:①偶函數(shù)的圖象一定與縱軸相交;②奇函數(shù)的圖象一定通過(guò)原點(diǎn);③f(x)=0(x∈R)既是奇函數(shù),又是偶函數(shù);④偶函數(shù)的圖象關(guān)于y軸對(duì)稱.其中正確的命題是________.解析:偶函數(shù)的圖象關(guān)于y軸對(duì)稱,不一定與y軸相交,①錯(cuò),④對(duì);奇函數(shù)當(dāng)x=0無(wú)意義時(shí),其圖象不過(guò)原點(diǎn),②錯(cuò),③對(duì).答案:③④9.①f(x)=x2(x2+2);②f(x)=xx;③f(x)=3x+x;④f(x)=1-x2x.以上函數(shù)中的奇函數(shù)是________.解析:(1)∵x∈R,∴-x∈R,又∵f(-x)=(-x)2[(-x)2+2]=x2(x2+2)=f(x),∴f(x)為偶函數(shù).(2)∵x∈R,∴-x∈R,又∵f(-x)=-x-x=-xx=-f(x), ∴f(x)為奇函數(shù).(3)∵定義域?yàn)閇0,+∞),不關(guān)于原點(diǎn)對(duì)稱,∴f(x)為非奇非偶函數(shù).(4)f(x)的定義域?yàn)閇-1,0)∪(0,1]即有-1≤x≤1且x≠0,則-1≤-x≤1且-x≠0,又∵f(-x)=1--x2-x=-1-x2x=-f(x).∴f(x)為奇函數(shù).答案:②④10.判斷下列函數(shù)的奇偶性:(1)f(x)=(x-1) 1+x1-x;(2)f(x)=x2+x x<0-x2+x x>0.解:(1)由1+x1-x≥0,得定義域?yàn)閇-1,1),關(guān)于原點(diǎn)不對(duì)稱,∴f(x)為非奇非偶函數(shù).(2)當(dāng)x<0時(shí),-x>0,則f(-x)=-(-x)2-x=-(-x2+x)=-f(x),當(dāng)x>0時(shí),-x<0,則f(-x)=(-x)2-x=-(-x2+x)=-f(x),綜上所述,對(duì)任意的x∈(-∞,0)∪(0,+∞),都有f(-x)=-f(x),∴f(x)為奇函數(shù).11.判斷函數(shù)f(x)=1-x2x+2-2的奇偶性.解:由1-x2≥0得-1≤x≤1.由x+2-2≠0得x≠0且x≠-4. ∴定義域?yàn)閇-1,0)∪(0,1],關(guān)于原點(diǎn)對(duì)稱.∵x∈[-1,0)∪(0,1]時(shí),x+2>0,
∴f(x)=1-x2x+2-2=1-x2x,∴f(-x)=1--x2-x=-1-x2x=-f(x),∴f(x)=1-x2x+2-2是奇函數(shù).12.若函數(shù)f(x)的定義域是R,且對(duì)任意x,y∈R,都有f(x+y)=f(x)+f(y)成立.試判斷f(x)的奇偶性.解:在f(x+y)=f(x)+f(y)中,令x=y(tǒng)=0,得f(0+0)=f(0)+f(0),∴f(0)=0.再令y=-x,則f(x-x)=f(x)+f(-x),即f(x)+f(-x)=0,∴f(-x)=-f(x),故f(x)為奇函數(shù).
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