
一、選擇題
設(shè)D,E,F(xiàn)分別為△ABC的三邊BC,CA,AB的中點(diǎn),則eq \(EB,\s\up14(→))+eq \(FC,\s\up14(→))=( )
A.eq \(AD,\s\up14(→)) B.eq \f(1,2)eq \(AD,\s\up14(→)) C.eq \f(1,2)eq \(BC,\s\up14(→)) D.eq \(BC,\s\up14(→))
已知O是正六邊形ABCDEF的中心,則與向量eq \(OA,\s\up14(→))平行的向量為( )
A.eq \(AB,\s\up14(→))+eq \(AC,\s\up14(→)) B.eq \(AB,\s\up14(→))+eq \(BC,\s\up14(→))+eq \(CD,\s\up14(→)) C.eq \(AB,\s\up14(→))+eq \(AF,\s\up14(→))+eq \(CD,\s\up14(→)) D.eq \(AB,\s\up14(→))+eq \(CD,\s\up14(→))+eq \(DE,\s\up14(→))
設(shè)向量a,b不共線,eq \(AB,\s\up14(→))=2a+pb,eq \(BC,\s\up14(→))=a+b,eq \(CD,\s\up14(→))=a-2b,若A,B,D三點(diǎn)共線,
則實(shí)數(shù)p的值為( )
A.-2 B.-1 C.1 D.2
莊嚴(yán)美麗的國旗和國徽上的五角星是革命和光明的象征.正五角星是一個(gè)非常優(yōu)美的幾何圖形,且與黃金分割有著密切的聯(lián)系.在如圖所示的正五角星中,以A,B,C,D,E為頂點(diǎn)的多邊形為正五邊形,且eq \f(PT,AT)=eq \f(\r(5)-1,2).下列關(guān)系中正確的是( )
A.eq \(BP,\s\up14(→))-eq \(TS,\s\up14(→))=eq \f(\r(5)+1,2)eq \(RS,\s\up14(→)) B.eq \(CQ,\s\up14(→))+eq \(TP,\s\up14(→))=eq \f(\r(5)+1,2)eq \(TS,\s\up14(→))
C.eq \(ES,\s\up14(→))-eq \(AP,\s\up14(→))=eq \f(\r(5)-1,2)eq \(BQ,\s\up14(→)) D.eq \(AT,\s\up14(→))+eq \(BQ,\s\up14(→))=eq \f(\r(5)-1,2)eq \(CR,\s\up14(→))
如圖,在直角梯形ABCD中,AB=2AD=2DC,E為BC邊上一點(diǎn),eq \(BC,\s\up14(→))=3eq \(EC,\s\up14(→)),F(xiàn)為AE的中點(diǎn),
則eq \(BF,\s\up14(→))=( )
A.eq \f(2,3)eq \(AB,\s\up14(→))-eq \f(1,3)eq \(AD,\s\up14(→)) B.eq \f(1,3)eq \(AB,\s\up14(→))-eq \f(2,3)eq \(AD,\s\up14(→)) C.-eq \f(2,3)eq \(AB,\s\up14(→))+eq \f(1,3)eq \(AD,\s\up14(→)) D.-eq \f(1,3)eq \(AB,\s\up14(→))+eq \f(2,3)eq \(AD,\s\up14(→))
如圖,在△ABC中,N為線段AC上靠近點(diǎn)A的三等分點(diǎn),點(diǎn)P在線段BN上且滿足:
eq \(AP,\s\up14(→))=(m+eq \f(2,11))eq \(AB,\s\up14(→))+eq \f(2,11)eq \(BC,\s\up14(→)),則實(shí)數(shù)m的值為( )
A.1 B.eq \f(1,3) C.eq \f(9,11) D.eq \f(5,11)
如圖,在等邊△ABC中,O為△ABC的重心,點(diǎn)D為BC邊上靠近B點(diǎn)的四等分點(diǎn),
若eq \(OD,\s\up14(→))=xeq \(AB,\s\up14(→))+yeq \(AC,\s\up14(→)),則x+y=( )
A.eq \f(1,12) B.eq \f(1,3) C.eq \f(2,3) D.eq \f(3,4)
P是△ABC所在平面上的一點(diǎn),滿足eq \(PA,\s\up14(→))+eq \(PB,\s\up14(→))+eq \(PC,\s\up14(→))=2eq \(AB,\s\up14(→)),若S△ABC=6,則△PAB面積為( )
A.2 B.3 C.4 D.8
已知圓心為O,半徑為1的圓上有不同的三個(gè)點(diǎn)A,B,C,其中eq \(OA,\s\up14(→))·eq \(OB,\s\up14(→))=0,存在實(shí)數(shù)λ,μ滿足eq \(OC,\s\up14(→))+λeq \(OA,\s\up14(→))+μeq \(OB,\s\up14(→))=0,則實(shí)數(shù)λ,μ的關(guān)系為( )
A.λ2+μ2=1 B.eq \f(1,λ)+eq \f(1,μ)=1 C.λμ=1 D.λ+μ=1
已知P,Q為三角形ABC中不同兩點(diǎn),若eq \(PA,\s\up14(→))+eq \(PB,\s\up14(→))+eq \(PC,\s\up14(→))=eq \(AB,\s\up14(→)),eq \(QA,\s\up14(→))+3eq \(QB,\s\up14(→))+5eq \(QC,\s\up14(→))=0,
則S△PAB:S△QAB為( )
A.eq \f(1,3) B.eq \f(3,5) C.eq \f(5,7) D.eq \f(7,9)
二、填空題
已知?ABCD的對角線AC和BD相交于O,且eq \(OA,\s\up14(→))=a,eq \(OB,\s\up14(→))=b,則eq \(DC,\s\up14(→))= ,eq \(BC,\s\up14(→))= .(用a,b表示)
已知S是△ABC所在平面外一點(diǎn),D是SC中點(diǎn),若eq \(BD,\s\up14(→))=xeq \(AB,\s\up14(→))+yeq \(AC,\s\up14(→))+zeq \(AS,\s\up14(→)),則x+y+z= .
在直角梯形ABCD中,∠A=90°,∠B=30°,AB=2eq \r(3),BC=2,點(diǎn)E在線段CD上,
若eq \(AE,\s\up14(→))=eq \(AD,\s\up14(→))+μeq \(AB,\s\up14(→)),則μ的取值范圍是
在△ABC中,已知AB⊥AC,AB=AC,點(diǎn)M滿足eq \(AM,\s\up14(→))=teq \(AB,\s\up14(→))+(1-t)eq \(AC,\s\up14(→)),若∠BAM=eq \f(π,3),則t= .
已知G是△ABC的重心,過點(diǎn)G作直線MN與AB,AC交于點(diǎn)M,N,且eq \(AM,\s\up14(→))=xeq \(AB,\s\up14(→)),eq \(AN,\s\up14(→))=yeq \(AC,\s\up14(→))(x,y>0),則3x+y的最小值是 .
\s 0 答案詳解
答案為:A.
解析:由題意得eq \(EB,\s\up14(→))+eq \(FC,\s\up14(→))=eq \f(1,2)(eq \(AB,\s\up14(→))+eq \(CB,\s\up14(→)))+eq \f(1,2)(eq \(AC,\s\up14(→))+eq \(BC,\s\up14(→)))=eq \f(1,2)(eq \(AB,\s\up14(→))+eq \(AC,\s\up14(→)))=eq \(AD,\s\up14(→)).
答案為:B.
解析:eq \(AB,\s\up14(→))+eq \(BC,\s\up14(→))+eq \(CD,\s\up14(→))=eq \(AD,\s\up14(→))=2eq \(AO,\s\up14(→))=-2eq \(OA,\s\up14(→)).
答案為:B.
解析:因?yàn)閑q \(BC,\s\up14(→))=a+b,eq \(CD,\s\up14(→))=a-2b,所以eq \(BD,\s\up14(→))=eq \(BC,\s\up14(→))+eq \(CD,\s\up14(→))=2a-b.又因?yàn)锳,B,D三點(diǎn)共線,
所以eq \(AB,\s\up14(→)),eq \(BD,\s\up14(→))共線.設(shè)eq \(AB,\s\up14(→))=λeq \(BD,\s\up14(→)),所以2a+pb=λ(2a-b),
所以2=2λ,p=-λ,即λ=1,p=-1.
答案為:A.
解析:由題意得,eq \(BP,\s\up14(→))-eq \(TS,\s\up14(→))=eq \(TE,\s\up14(→))-eq \(TS,\s\up14(→))=eq \(SE,\s\up14(→))=eq \f(\(RS,\s\up14(→)),\f(\r(5)-1,2))=eq \f(\r(5)+1,2)eq \(RS,\s\up14(→)),所以A正確;
eq \(CQ,\s\up14(→))+eq \(TP,\s\up14(→))=eq \(PA,\s\up14(→))+eq \(TP,\s\up14(→))=eq \(TA,\s\up14(→))=eq \f(\r(5)+1,2)eq \(ST,\s\up14(→)),所以B錯(cuò)誤;
eq \(ES,\s\up14(→))-eq \(AP,\s\up14(→))=eq \(RC,\s\up14(→))-eq \(QC,\s\up14(→))=eq \(RQ,\s\up14(→))=eq \f(\r(5)-1,2)eq \(QB,\s\up14(→)),所以C錯(cuò)誤;
eq \(AT,\s\up14(→))+eq \(BQ,\s\up14(→))=eq \(SD,\s\up14(→))+eq \(RD,\s\up14(→)),eq \f(\r(5)-1,2)eq \(CR,\s\up14(→))=eq \(RS,\s\up14(→))=eq \(RD,\s\up14(→))-eq \(SD,\s\up14(→)),若eq \(AT,\s\up14(→))+eq \(BQ,\s\up14(→))=eq \f(\r(5)-1,2)eq \(CR,\s\up14(→)),
則eq \(SD,\s\up14(→))=0,不合題意,所以D錯(cuò)誤.故選A.
答案為:C.
解析:eq \(BF,\s\up14(→))=eq \(BA,\s\up14(→))+eq \(AF,\s\up14(→))=eq \(BA,\s\up14(→))+eq \f(1,2)eq \(AE,\s\up14(→))=-eq \(AB,\s\up14(→))+eq \f(1,2)eq \b\lc\(\rc\)(\a\vs4\al\c1(\(AD,\s\up14(→))+\f(1,2)\(AB,\s\up14(→))+\(CE,\s\up14(→))))=-eq \(AB,\s\up14(→))+eq \f(1,2)eq \(AD,\s\up14(→))+eq \f(1,2)eq \(AB,\s\up14(→))+eq \f(1,3)eq \(CB,\s\up14(→))
=-eq \(AB,\s\up14(→))+eq \f(1,2)eq \(AD,\s\up14(→))+eq \f(1,4)eq \(AB,\s\up14(→))+eq \f(1,6)(eq \(CD,\s\up14(→))+eq \(DA,\s\up14(→))+eq \(AB,\s\up14(→)))=-eq \f(2,3)eq \(AB,\s\up14(→))+eq \f(1,3)eq \(AD,\s\up14(→)).
答案為:D.
解析:eq \(AP,\s\up14(→))=(m+eq \f(2,11))eq \(AB,\s\up14(→))+eq \f(2,11)eq \(BC,\s\up14(→))=(m+eq \f(2,11))eq \(AB,\s\up14(→))+eq \f(2,11)(eq \(AC,\s\up14(→))-eq \(AB,\s\up14(→)))=meq \(AB,\s\up14(→))+eq \f(2,11)eq \(AC,\s\up14(→)),
設(shè)eq \(BP,\s\up14(→))=λeq \(BN,\s\up14(→))(0≤λ≤1),則eq \(AP,\s\up14(→))=eq \(AB,\s\up14(→))+λeq \(BN,\s\up14(→))=eq \(AB,\s\up14(→))+λ(eq \(AN,\s\up14(→))-eq \(AB,\s\up14(→)))=(1-λ)eq \(AB,\s\up14(→))+λeq \(AN,\s\up14(→)),
因?yàn)閑q \(AN,\s\up14(→))=eq \f(1,3)eq \(AC,\s\up14(→)),所以eq \(AP,\s\up14(→))=(1-λ)eq \(AB,\s\up14(→))+eq \f(1,3)λeq \(AC,\s\up14(→)),
則eq \b\lc\{\rc\ (\a\vs4\al\c1(m=1-λ,,\f(2,11)=\f(1,3)λ,))解得eq \b\lc\{\rc\ (\a\vs4\al\c1(λ=\f(6,11),,m=\f(5,11),))故選D.
答案為:B.
解析:設(shè)點(diǎn)E為BC的中點(diǎn),連接AE,可知O在AE上,
由eq \(OD,\s\up14(→))=eq \(OE,\s\up14(→))+eq \(ED,\s\up14(→))=eq \f(1,3)eq \(AE,\s\up14(→))+eq \f(1,4)eq \(CB,\s\up14(→))=eq \f(1,6)(eq \(AB,\s\up14(→))+eq \(AC,\s\up14(→)))+eq \f(1,4)(eq \(AB,\s\up14(→))-eq \(AC,\s\up14(→)))=eq \f(5,12)eq \(AB,\s\up14(→))-eq \f(1,12)eq \(AC,\s\up14(→)),
故x=eq \f(5,12),y=-eq \f(1,12),x+y=eq \f(1,3).故選B.
答案為:A.
解析:∵eq \(PA,\s\up14(→))+eq \(PB,\s\up14(→))+eq \(PC,\s\up14(→))=2eq \(AB,\s\up14(→))=2(eq \(PB,\s\up14(→))-eq \(PA,\s\up14(→))),∴3eq \(PA,\s\up14(→))=eq \(PB,\s\up14(→))-eq \(PC,\s\up14(→))=eq \(CB,\s\up14(→)),∴eq \(PA,\s\up14(→))∥eq \(CB,\s\up14(→)),
且方向相同,∴eq \f(S△ABC,S△PAB)=eq \f(BC,AP)=eq \f(|\(CB,\s\up14(→))|,|\(PA,\s\up14(→))|)=3,∴S△PAB=eq \f(S△ABC,3)=2.
答案為:A.
解析:解法1:取特殊點(diǎn),取C點(diǎn)為優(yōu)弧AB的中點(diǎn),
此時(shí)由平面向量基本定理易得λ=μ=eq \f(\r(2),2),只有A符合.故選A.
解法2:依題意得|eq \(OA,\s\up14(→))|=|eq \(OB,\s\up14(→))|=|eq \(OC,\s\up14(→))|=1,-eq \(OC,\s\up14(→))=λeq \(OA,\s\up14(→))+μeq \(OB,\s\up14(→)),兩邊平方得1=λ2+μ2.故選A.
答案為:B.
解析:令D為AC的中點(diǎn),eq \(PA,\s\up14(→))+eq \(PB,\s\up14(→))+eq \(PC,\s\up14(→))=eq \(AB,\s\up14(→)),化為eq \(PA,\s\up14(→))+eq \(PC,\s\up14(→))=eq \(AB,\s\up14(→))-eq \(PB,\s\up14(→)),即2eq \(PD,\s\up14(→))=eq \(AP,\s\up14(→)),
可得AC=3AP,且點(diǎn)P在AC邊上,則S△PAB=eq \f(1,2)S△ABC,設(shè)點(diǎn)M,N分別是AC,AB的中點(diǎn),
則由eq \(QA,\s\up14(→))+3eq \(QB,\s\up14(→))+5eq \(QC,\s\up14(→))=0可得2eq \(QM,\s\up14(→))+6eq \(QN,\s\up14(→))+eq \(QC,\s\up14(→))=0,設(shè)點(diǎn)T是CN的中點(diǎn),則2eq \(QM,\s\up14(→))+5eq \(QN,\s\up14(→))+2eq \(QT,\s\up14(→))=0,
設(shè)點(diǎn)S是MT的中點(diǎn),則4eq \(QS,\s\up14(→))+5eq \(QN,\s\up14(→))=0,因此可得S△QAB=eq \f(5,9)S△ABC,所以S△PABS△QAB=eq \f(3,5),故選B.
答案為:b-a,-a-b.
解析:如圖,eq \(DC,\s\up14(→))=eq \(AB,\s\up14(→))=eq \(OB,\s\up14(→))-eq \(OA,\s\up14(→))=b-a,eq \(BC,\s\up14(→))=eq \(OC,\s\up14(→))-eq \(OB,\s\up14(→))=-eq \(OA,\s\up14(→))-eq \(OB,\s\up14(→))=-a-b.
答案為:0.
解析:依題意得eq \(BD,\s\up14(→))=eq \(AD,\s\up14(→))-eq \(AB,\s\up14(→))=eq \f(1,2)(eq \(AS,\s\up14(→))+eq \(AC,\s\up14(→)))-eq \(AB,\s\up14(→))=-eq \(AB,\s\up14(→))+eq \f(1,2)eq \(AC,\s\up14(→))+eq \f(1,2)eq \(AS,\s\up14(→)),
因此x+y+z=-1+eq \f(1,2)+eq \f(1,2)=0.
答案為:[0,eq \f(1,2)].
解析:由題意可求得AD=1,CD=eq \r(3),所以eq \(AB,\s\up14(→))=2eq \(DC,\s\up14(→)).
∵點(diǎn)E在線段CD上,∴eq \(DE,\s\up14(→))=λeq \(DC,\s\up14(→))(0≤λ≤1).
∵eq \(AE,\s\up14(→))=eq \(AD,\s\up14(→))+eq \(DE,\s\up14(→)),又eq \(AE,\s\up14(→))=eq \(AD,\s\up14(→))+μeq \(AB,\s\up14(→))=eq \(AD,\s\up14(→))+2μeq \(DC,\s\up14(→))=eq \(AD,\s\up14(→))+eq \f(2μ,λ)eq \(DE,\s\up14(→)),
∴eq \f(2μ,λ)=1,即μ=eq \f(λ,2).∵0≤λ≤1,∴0≤μ≤eq \f(1,2).即μ的取值范圍是[0,eq \f(1,2)].
答案為:eq \f(\r(3)-1,2).
解析:由題意可得eq \(AM,\s\up14(→))=teq \(AB,\s\up14(→))+eq \(AC,\s\up14(→))-teq \(AC,\s\up14(→)),所以eq \(AM,\s\up14(→))-eq \(AC,\s\up14(→))=teq \(AB,\s\up14(→))-teq \(AC,\s\up14(→)),即eq \(CM,\s\up14(→))=teq \(CB,\s\up14(→)),
所以eq \(CM,\s\up14(→))與eq \(CB,\s\up14(→))共線,即B,M,C三點(diǎn)共線,且t=eq \f(|\(CM,\s\up14(→))|,|\(CB,\s\up14(→))|).
又由條件知|eq \(BC,\s\up14(→))|=eq \r(2)|eq \(AC,\s\up14(→))|,所以t=eq \f(|\(CM,\s\up14(→))|,\r(2)|\(AC,\s\up14(→))|).
在△ABC中,由正弦定理知eq \f(|\(CM,\s\up14(→))|,|\(AC,\s\up14(→))|)=eq \f(sin30°,sin105°)=eq \f(\f(1,2),\f(\r(6)+\r(2),4))=eq \f(2,\r(6)+\r(2)),
所以t=eq \f(2,\r(2)×?\r(6)+\r(2)?)=eq \f(\r(3)-1,2).
答案為:eq \f(4+2\r(3),3).
解析:如圖,∵M(jìn),N,G三點(diǎn)共線,∴eq \(MG,\s\up14(→))=λeq \(GN,\s\up14(→)).
∴eq \(AG,\s\up14(→))-eq \(AM,\s\up14(→))=λ(eq \(AN,\s\up14(→))-eq \(AG,\s\up14(→))).∵G是△ABC的重心,∴eq \(AG,\s\up14(→))=eq \f(1,3)(eq \(AB,\s\up14(→))+eq \(AC,\s\up14(→))).
∴eq \f(1,3)(eq \(AB,\s\up14(→))+eq \(AC,\s\up14(→)))-xeq \(AB,\s\up14(→))=λyeq \(AC,\s\up14(→))-eq \f(1,3)(eq \(AB,\s\up14(→))+eq \(AC,\s\up14(→))).∴eq \b\lc\{\rc\ (\a\vs4\al\c1(\f(1,3)-x=-\f(1,3)λ,,\f(1,3)=λy-\f(1,3)λ,))
整理得(3x-1)·(3y-1)=1;結(jié)合圖象可知eq \f(1,2)≤x≤1,eq \f(1,2)≤y≤1;
令3x-1=m,3y-1=neq \f(1,2)≤m≤2,eq \f(1,2)≤n≤2,則mn=1,x=eq \f(1+m,3),y=eq \f(1+n,3).
故3x+y=1+m+eq \f(1+n,3)=eq \f(4,3)+m+eq \f(n,3)≥eq \f(4,3)+2eq \r(\f(1,3)mn)=eq \f(4,3)+eq \f(2\r(3),3),
當(dāng)且僅當(dāng)m=eq \f(\r(3),3),n=eq \r(3)時(shí)等號成立.
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