举报
cyg25gz
1.BC,BPΪx,zὨռֱϵ B(000),C(200),P(002),A(220),E(10,1),M(110).PB=BC,EΪPCе,BEPC,BE*AC=(101)*(0-20)=0BEAC,BEƽPAC. 2.FPAϣ2PF=FA,BF=(2/3)BP+(1/3)BA=(2/3)(002)+(1/3)(220)=(2/32/34/3).ƽBEFķΪn1=(x,y,1),n1*BF=0x+y+2=0,n1*BE=0x+1=0,x=y=-1,n1=(-1,-1,1),CM=(-110),CM*n1=0CMƽBEFڣCMƽBEF. 3.ƽABCķn2=(0,0,1),ƽABCBEFɵĶǵƽǣǣֵ=|cos|=1/3=3/3.4AF=BF-BA=(2/32/34/3)-(220)=(-4/3-4/34/3),ֱAFBEFɽǵֵ=cos=(4/3)/4=1/3.