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1812֣ ͼʾABCA1B1C1 УAB=AC=a?BAC?90
A1 C1
A1ڵABCϵӰΪBCߵеM.
1 ֤BC?ƽA1AM; 2 CA1B1C1Ϊ
B1
0߶ѧԾ
ѡ 90֣
ע1ǰؽԼ༶Ծܷڹ涨ĵط
33a 12A C
Ҫ 2ʱɫֱʻԲֱдԾ涨ĵط
17 18 19 20 21 22 ⣨ÿ4֣16֣
13.ֱ??l??,C??,D??,CDlϵӰֱAB
AB=AC=BD=5cmCD=53 cm. 14.ĶԽ߳Ϊ2ȫֵΪ 4 .
15.ABC?A1B1C1УEFֱΪABACе㣬ƽEB1C1Fֳ֣ôС֮Ϊ 75
16.ABCDΪVBCijΪa?ABC?DBCֱΪS1S2A?BC?DɽǵĴС?ôsin?
3aV2SS
12⣺
1712֣ͼ?ABCRt?BCDֱǣ
?BCD?900,?CBD?300. (1) DABCĴС A (2) ACBDɽǵĴС. B C
D
(1)arctan2 (2)arccos334
ѧ 1ҳ4ҳ ABB1A1ABCǵĴС.
B M
A(1)֤AM?AB=AC,MΪBCе㣬?AM?BC, 1 C1A1ڵABCϵӰΪBCߵеM.
B1
? A1M?BC, BC?ƽA1AM
(2)⣺ȡABеNMN,A1N, ? AB=AC,
A C
?BAC?900 ?MN?AB,A1M ?ƽABC N
? A1N?AB,A1NMǵƽǣ B M ?
VC?A1B1C1?VA1?ABC?1123?2aAM?312a3 ?A3111M=2 MN=2a ? tan?A1NM?3,?ABB1A1ABCΪ600
19ͼ֪PABCУPA?ƽABCPA=3,AC=4,PB=PC=BC.
(1) PABCV
P (2) AƽPBCĴ߶AE,AEij 1V?5394 23135 A
C
B
ѧ 2ҳ4ҳ
2012֣ ⳤΪ4ABCDA1B1C1D1,OA1B1C1D1ģ2PCC1ϣCC1=4CP
ֱAPƽBCCD1
C1
1B1ɵĽǵĴС
O ÷Ǻʾ;
OƽD1APϵӰH֤
A1 B1
D1H?AP;
H
P PƽABD1ľ룮 ⣺BP?APBΪǣ
D C
ã?APBarctan41717
A B ֤D1O?ƽD1APC1,涨D1H?AP;
(3)BC1,PPQ?BC1Q, ֤PQΪ룬??PC1Q=450, PC1=3
PQ=322
2114֣ͼ֪ABCD;ACEFE ڵƽ滥ഹֱ
AB=2,AF=1,M߶EFе.
(1) ֤AM//ƽBDE; M (2) ADFBĴС
C S F B
(3) ߶ACȷһPʹPFBCɵĽΪ600. P
Q
1֤BDOOE
O ɵıAOEMƽıΣƳAM//ƽBDE;
D
A AS?DF,BS֤?BSAΪǵƽ 600 3CP=t0?t?2
PQ?ABQPQ//AD, ?PQ?AB,PQ?AF, ?PQ?ƽABF? PQ?QF, Rt?PQFУ?FPQ=600
,PF=2PQ
??PAQΪֱΣ?PQ=
22(2?t) ѧ 3ҳ4ҳ ??PAFΪֱΣ?PF?(2?t)?1
?(2?t)2?1?2?22(2?t) ?t=1t=3ȥPACе㡣 2212֣ͼABCDADQPڵƽ洹ֱADQPPDۣʹ÷ۺQBCϣAB=1,PA=h,AD?y
(1) yhĺʽ
(2) yȡСֵʱָQλãʱADƽPDQɵĽǣ (3) ڣ2£PADQİ뾶.
ĿͼABCDADQPڵƽ洹ֱADQPPDۣʹ÷ۺQBCеϣAB=1,PA=2
(1) ADƽPDQɵĽǣ2PADQڽİ뾶. P
Q
P
A D
A D
B
C
B
Q
C
ƣ1y?h2h2?1(h?1); 2Q Ϊ BCе㣬300; (3) r?2?22
ѧ 4ҳ4ҳ
Ҫ