在空间四边形ABCD中,M、N、P、Q分别是四边上的点,且满足====k. (1)求证:M、N、P、Q共面. (2)当对角线AC=a,BD=b,且MNPQ是正方形时,求AC、BD所成的角及k的值(用a,b表示) 答案:解析:(1)∵ ==k ∴ MQ∥BD,且= ∴ == ∴ MQ=BD 又 ==k ∴ PN∥BD,且= ∴ ==从而NP=BD ∴ MQ∥NP,MQ,NP共面,从而M、N、P、Q四点共面. (2)∵ =,= ∴ ==,= ∴ MN∥AC,又NP∥BD. ∴ MN与NP所成的角等于AC与BD所成的角. ∵ MNPQ是正方形,∴ ∠MNP=90° ∴ AC与BD所成的角为90°, This training program can give you a lift at work, ____ increase your income by 40%.
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