由(1)知F1(-2,0),F2(2,0),3∴直线AF1方程为y=(x+2),即3x-4y+6=04设点F2(2,0)关于直线AM的对称点F2′(x0,y0),y01=-kx0-2则y0x0+2-3=k?-2?22解之得F2′(-6k+2k2+26,).221+k1+k∵直线AF1与直线AF2关于直线AM对称,∴点F2′在直线AF1上.-6k+2k2+26即3×-4×+6=0.221+k1+k1解得k=-或k=2.2由图形知,角平分线所在直线方程斜率为正,1∴k=-(舍去).2故∠F1AF2的角平分线所在直线方程为2x-y-1=0.法三:∵A(2,3),F1(-2,0),F2(2,0),→→∴AF1=(-4,-3),AF2=(0,-3),→→AF1AF211∴+=(-4,-3)+(0,-3)→→3|AF2||AF2|54=-(1,2),5∴kl=2,∴l:y-3=2(x-2),即2x-y-1=0.20、(Ⅰ)证明:取AB的中点O,连接PO,CO,AC.∵AP?BP,∴PO?AB
又四边形ABCD是菱形,且?BCD?120?,∴VACB是等边三角形,∴CO?AB又COIPO?O,∴AB?平面PCO,又PC?平面PCO,∴AB?PC
(Ⅱ)由AB?PC?2,AP?BP?∴OP?OC?PC,OP?OC
2
2
2
2,易求得PO?1,OC?3,以O为坐标原点,以OC,OB,OP分别为x轴,y轴,z轴建立空间直坐标系O?xyz,则B(0,1,0),C(3,0,0),P(0,0,1),D(3,?2,0),????????????BC?(3,?1,0)PC?(3,0,?1)∴,,DC?(0,2,0)
??????????????设平面DCP的一个法向量为n1?(1,y,z),则n1?PC,n1?DC,??????
????n1?PC?3?z?0
∴???????,∴z?3,y?0,∴n1?(1,0,3)??n1?DC?2y?0
?????????????????
设平面BCP的一个法向量为n2?(1,b,c),则n2?PC,n2?BC,???????
?????n2?PC?3?c?0
∴???,∴c?3,b?3,∴n2?(1,3,3)???????n2?BC?3?b?0
??????????n?n2427???∴cos?n1,n2????1??,7|n1|?|n2|2?7∵二面角B?PC?D为钝角,∴二面角B?PC?D的余弦值为?21、(1)f(x)?x?3x22、b??
3227.7
(2)最大值9,最小值?421
,c??2。m?(2,??)2