Question

设A,B,C,D是空间内不公面的四点,且满足,则是

Answer 1

∵AB•AC=0,AC•AD=0,AB•AD=0,∴AB⊥AC,AC⊥AD,AB⊥AD,设 AB=a,AC=b,AD=c,则BC=a2+b2,CD=b2+c2,BD=c2+a2,△BCD中,有余弦定理得cosB=a2a2+b2•a2+c2＞0,同理可证,cosC＞0,cosD＞0,∴B,C,D都是锐...