当前位置:淘百问>百科问答>如图正方体$ABCD-A_{1}B_{1}C_{1}D_{1}$棱长为$a$,下列结论错误的是( )

如图正方体$ABCD-A_{1}B_{1}C_{1}D_{1}$棱长为$a$,下列结论错误的是( )

2023-08-18 15:38:06 编辑:join 浏览量:577

如图正方体$ABCD-A_{1}B_{1}C_{1}D_{1}$棱长为$a$,下列结论错误的是(  )

对于$A$:因为$A_{1}D_{1}$∥$AD$∥$BC$,且$A_{1}D_{1}=AD=BC$,所以四边形$A_{1}D_{1}CB$是平行四边形,所以$A_{1}B$∥$CD_{1}$,又因为$CD_{1}$⊄平面$A_{1}C_{1}B$,$A_{1}B\subset $平面$A_{1}C_{1}B$,所以$CD_{1}$∥平面$A_{1}C_{1}B$,同理$D_{1}A$∥平面$A_{1}C_{1}B$,又$CD_{1}\cap D_{1}A=D_{1}$,$CD_{1}\subset $平面$ACD_{1}$,$D_{1}A\subset $平面$ACD_{1}$,所以平面$ACD_{1}$∥平面$A_{1}C_{1}B$,故$A$正确;对于$B$:易得$AB\bot $平面$ADD_{1}A_{1}$,所以$AB\bot A_{1}D$,又$A_{1}D\bot AD_{1}$,又$AB\cap AD_{1}=A$,所以$A_{1}D\bot $平面$ABD_{1}$,所以$A_{1}D\bot BD_{1}$,同理可证$C_{1}D\bot BD_{1}$,又$A_{1}D\cap C_{1}D=D$,所以$BD_{1}\bot $平面$A_{1}C_{1}D$,故$B$正确;对于$C$:由正方体$ABCD-A_{1}B_{1}C_{1}D_{1}$棱长为$a$,可得$AB_{1}=B_{1}C=AC=\sqrt{2}a$,所以$\triangle AB_{1}C$为等边三角形,所以$\angle AB_{1}C=60^{\circ}$,$AB_{1}$与$B_{1}C$成$60^{\circ}$角,故$C$正确;对于$D$:${V}_{A-BD{D}_{1}}={V}_{{D}_{1}-ABD}=\frac{1}{3}\times \frac{1}{2}\times AB\times AD\times DD_{1}=\frac{1}{6}a^{3}$,故$D$错误.故选:$D$.

标签:正方体,ABCD,棱长

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