/ GIfu roAN vi' vAr l
uor nAr rotrN s.rl oAp AN
1oi aAng tuAn TH&TT s6 4s7, thting 7 ndm 2015) C6ch gidi cta b4n Nam sai,ban Binh ding.
B1n Nam sai d ch5: 56 c6ch chia 8 dQi thdnh 2 bang
ld C;.Ct. Khi bAn Nam chon C).C! cdch, c6 nghTa ld
ban dd chon trung ldp clc trucrng hqp vi ttt t6y
C! cdch c6 nghia dd chgn 6t cA cilc truong hqp phdn
).i:.
biet can sdp x6p vdo hai bing A, B. Vi du: khi chgn Cra thi c6 trudng hqp b6ng A c6 4 d.Qi a, b, c, d;bing
B c6 4 dQi e,f, g, h vd cffng d5 c6 trudng hqpb/r;rg Ac6 4 tlQi e,.f, g, h;bdng B c6 4 dQi a, b, c, d. Nhu c6 4 tlQi e,.f, g, h;bdng B c6 4 dQi a, b, c, d. Nhu
vf,y kh6ng cAn nhdn th6m Cl.
NhQn xit: 1) Tuy6n ducrng hai b4n sau dd phitt hiQn dtng
sai 16m: Hung YOn: Tri€u Ninh Ngdn, 10A9, THPT
Duong Qu6ng Hdm, Vdn Giang. NghQ An: Hi Thanh
Tirng, 12C1, THPT Kim Li6n, Nam Edn.
KIHIVI
CHi Co
3 TIfiP TIIYTII OHUNG I
-
^()f rongb,u6i 6n tdp ve ducrng tron. Hinh.hoc lope, 10. thay gi6o ra bdi torin: "Viet PT riep ruyen e, 10. thay gi6o ra bdi torin: "Viet PT riep ruyen
chung ctia hai drdng trdn
(Cr):t +f -4r-5=0 (Q):f +f +k-6y+16:0." Ldi gini cria b4n Y€n vdb1n Phong nhu sau;
Ldi gidi cfiu YAn. (C,) cO 6m I,(2;0) b5n kffi
Rr =3; (C.) IAm Ir(-4;3), ban kinh h R2 =3. Goi tii5ptuyi5nchungctra (C,) ve G) h A:ax+|ry+c=O, (dU,,N= R, a1 +b2+0.Khit16 l [dt1,.At=R, '' )2o + rl I i I -?
_ lffi -' .^[oo, +4ac +c2 =9a2 +9h2
- ll-0, +3b + cl " - ll-+a+3b+ cl=l2a+cl
l:=1
| ,la2 +b2
* THI: {la')++ac+c'2=9a2 +9U
"_l+ta, -4ar-c2 =0
l-4a+3b+c=2a+c 'lb=2oChon b :2 th\ a=l vd C +k-41=0 Chon b :2 th\ a=l vd C +k-41=0
e c = -2t 3.v5. Ta tlugc hai ti6p tuydn chung ld x +2y -21 3J5 = 0.
* -fH2, {M +kr+d =9a2 +98 ,_!+*+e =5d +9A
l-4a+3h+c=-2tt-t''' l3b=2a-2cChon b=4 thi Chon b=4 thi t+*+r, =5a2 +144 ^[4{6+c)c+cz -5(6+c)2 +144 [a=6+c - la=6+c l36c+324:0 [c=-9 <>< <>{ la=6+t. " [o=-3'
Ta ilugc tiep hryen chung
-3x + 4y-9 = 0 e 3x - 4y+9 = 0.
Vfy c6 3 ti6p tuy6n chung giira (C, ) vi (C) lit
x +2y -2t3vE = 0. 3x - 4y+ 9 = 0.
Ldi gi,rti crta Phong. (C,) cO tdm I,(2;0) b6n kinh
Rr =3; (Cr) tam Ir(4;3), b6n kinh h & =3. Gqiti6p tuy6n chung cira (Cr), (Cr) ld A : y = kx + m ti6p tuy6n chung cira (Cr), (Cr) ld A : y = kx + m
a kx - y + m:0. Khi d6 {d,u., 1' = I ld(r,,L) = R2 l+k'++km+m2 =9k2 +9 ollro +ml=l_-+*_3+ml [4m, - Bm-,41=o l--zxzJi I ,,,. ,. _u lnt= -, -10=-* o1,- t' l2
Ta duo. c hai tiep tuy6n chung ,, I Z t 2]3,J5 v = -- r + t-, r +2! -2fiJ5 =0. J 2" 2 -' * TrI2: [+*' + +rm + m2 =9k2 +9 l2k+n=4k+3-m (s {le* -zt =o l^ = o <>< , <>< l2m=2k*3 I k_3' Ta du-o. c ti6p ruyen ctrung la\ 4
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