(a) a;
(c) ayfl ; Trdldi (d).
HOATDQNG 2
2. Hirdng dan tra ldi cau hoi va bai tap on tap chUdng 1 Bai 1. Hudng ddn.
+ Xem lai cac khai niem da dien la gi?
+ Khai niem mat va dinh ciia da dien.
Bai 2. Hudng ddn.
+ Xem lai cac khai niem da dien la gi?
+ Khai niem mat va dinh cua da dien.
Vf du : Hinh tao bdi hai binh chii nhat
Bai 3. Hudng ddn.
+ Xem lai cac khai niem vd khdi da didn Idi.
GV tu cho HS neu vi du.
Bai 4. Hudng ddn.
+ Xem lai cac khai niem thd tfch khdi chdp va khdi lang tru.
+ Mdl quan he giiia chiing.
Bai 5. Hudng ddn.
+ Xem lai cac khai niem : Hinh chie'u vudng gdc ciia dudng thing tren mat phang.
+ Dinh If vd thd tich hinh chdp.
Hoat ddng ciia GV Hoat ddng ciia HS Cdu hdi 1
Tinh thd tich khdi chdp OABC.
Cdu hoi 2 Tfnh OE'
Cdu hdi 3 Tinh AE.
Cdu hdi 4
Tfnh didn tich tam giac ABC.
Ggi y trd ldi cdu hdi 1
^(OABC) = g ^ b c
Ggi y trd ldi cdu hdi 2
^ . 1 1 1 Taco j = ^ + -^
OE^ b^ c^
2 7
Txx 66 ta cd OE^ = ^ ^ b + c Ggi y trd ldi cdu hdi 3
.2„2
Tacd A E ^ = O E 2 + a 2 = ^ - + a^
b^+c^
Tit doa ta cd :
AE = a V + b V + c V b^+c^
Ggi y trd ldi cdu hdi 4 S = -AE.BC
2
' . 2 . 2 , u2„2 , „2„2
1 l a ^ b ^ ^ b V ^ c X / b ^ ^ c ^ b^+c^
Cdu hdi 5 Tinh OH
4^ a V + b V + c V
Ggi y trd ldi cdu hdi 5
3V abc 0 H =
V^2^^^c2+cV
Bai 6. Hudng ddn.
+ Xem lai cac khai niem : Hinh chdp tam giac ddu + Dinh If vd thd tfch hinh chdp.
+ van dung Bai tap 4 muc 3 SGK.
s
cau a.
Hoat ddng cua GV Cdu hdi 1
van dung bai toan 4 trong SGK hay vie't ti sd hai thd tfch.
Cdu hdi 2 TfnhAE.
Cdu hdi 3 Tfnh AH.
Hoat ddng ciia HS Ggi y trd ldi cdu hdi I
^(SDBC) _ SD.SB.SC _ SD V(sABC) SA.SB.SC SA Ggi y trd ldi cdu hdi 2
2
Ggi y trd ldi cdu hdi 3 AU 2 . „ aV3 A H - - A E - ^ .
3 3
Cdu hdi 4
Tfnh SA, tuf dd suy ra do dai cua cac canh bdn.
Cdu hdi 5 Tfnh SD.
Cdu hdi 6
Tfnh ti sd hai the tfch.
Ggi y trd ldi cdu hdi 4 SA = AH : cosdO" = ^ ^
3
Cac canh ben cd do dai bing nhau va
^. 2aV3
bang — ^
Ggi y trd ldi cdu hdi 5 Ta cd
AD = AB.cosSAB a aV3 -a.- 2a V3
Tit dd ta cd
SD = S A - A D : _ 5 a ^
12
2aV3 aV3
Ggi y trd ldi cdu hdi 6
SA _ 2aV3 12 ^ 5 S D " 3 " 5 3 7 3 " 8 Ta cd
caub.
Hoat ddng ciia GV Cdu hdi 1
TfnhSH.
Cdu hdi 2
Tfnh thd tfch hinh chdp S.ABC.
Hoat ddng cua HS Ggi y trd ldi cdu hdi I SH = AH.tandO" = — 4 Ggi y trd ldi cdu hdi 2
12
Cdu hdi 3
Tfnh thd tfch hinh chdp S.SBC.
Ggi y trd ldi cdu hdi 3
V ' = V 3
96
Bai 7. Hudng ddn. Six dung tfnh chit hinh chieu trong khdng gian. Cdng thiic tfnh thd tfch.
S
Ke SH ± mp(ABC), HE 1 AB, HF 1 BC va HJ 1 AC.
Hoat ddng cua GV Cdu hdi I
Em cd nhan xet gi vd SE, SF va SJ.
Cdu hdi 2
Tfnh chu vi tam giac ABC.
Cdu hdi 3 Tfnh HE.
Hoat ddng cua HS Ggi y trd ldi cdu hdi I
Vi cac gdc SEH,SFH, SJH bing nhau nen : SE = SF = SJ.
Goi y trd ldi cdu hdi 2
Chu vi tam giac ABC la : 18a; nita chu vi la 9a.
Ggi y trd loi cdu hdi 3
^AABC ^ P-HE .
Ta cd p = 9a, S^^gc - 6V6a
rr^v ô . . . ITT: ^AABC 2a\/6a Tu do ta CO : HE = =
P 3
Cdu hdi 4 Tfnh SH.
Cdu hdi 5 TfnhV
Ggi y trd ldi cdu hdi 4
Ta cd SH = HE tandO" = 2V2a . Ggi y trd ldi cdu hdi 5
V = 8V3a^
Bai 8. Hudng ddn. Six dung tfnh cha't hinh chie'u trong khdng gian. Cdng thiic tfnh thd tfch.
s
Ke SH 1 mp(ABC), HE 1 AB, HF 1 BC va HJ 1 AC.
Hoat ddng ciia GV Cdu hdi I
Cdu hdi 2
Tfnh SB va SB'
Hoat ddng cua HS Ggi y trd ldi cdu hdi 1 V = - a b c .
6
Ggi y trd ldi cdu hdi 2
Ta cd SA^ = SB'.SB hay SB' = SB Tacd SB = Va^+c^ Tit dd t a c d :
c2 S B ' -
Va2+c2
Cdu hdi 3
Tinh SD va SD'
Cdu hdi 4
Tfnh SC va S C
Cdu hdi 5
Tfnh thd tfch khdi chdp SAB'C'D'
Ggi y trd ldi cdu hdi 3 Tuong tu ta cd :
9
SB = Vb2+c2 SB' = - ^ = ^ = = Vc + D Ggi y trd ldi cdu hdi 4
SC ± A C
SC = Va^+b^+c^ ;
S C - c2
V a 2 + b 2 + c 2 Ggi y trd ldi cdu hdi 5 Tacd
% A B ' C D ) SA.SB'.SC'.SD' V SA.SB.SC.SD Tii dd ta tfnh dugc thd tfch khdi chdp S A B ' C ' D '
Bai 9. Hudng ddn. Six dung tfnh chat hinh chie'u trong khdng gian. Cdng thiic tinh the tfch.
Xem hinh ve
Hoat ddng ciia GV Cdu hdi I
Chung minh SM Imp(AEMF)
Cdu hdi 2
Tfnh SB va SB'
Cdu hdi 3 TfnhEF.
Cdu hdi 4
Tfnh SC va SC
Cdu hdi 5 Tfnh AM.
Cdu hdi 6
TinhV(sAEMF)'
Hoat ddng ciia HS Ggi y trd ldi cdu hdi I
Ta cd tam giac SAC la tam giac ddu canh aV2 , do dd AM 1 SC.