Voaor DE
Voesc >.. nti (t)
Votoe
Goi O1, O212n lucrt li tAm c6c dudng trdn noi
ti6.p LOBK, LOCK' Ndi KOr, KO2 chring cat
OB, OC theo thf tu tai P v) Q. Vi OPQ = 6119
= 450 nen tam gi6c OPQ vu6ng can tai O' Theo
tinh chat dudng phAn gi6c trong tam gi6c thi
OrK
=OU ,
OrP OP
mi oP = oQ.clan den ++ =9{ ,uv ,n
OtP OzQ
Op2llPQ. VAY tam gi6c OMN vu6ng cAn
tai O. Cung tir dAy ta thdy LOMOT = LOKOT
) OM = OK. T5m lai OM = ON = OK'
Do S66a,y = Lou.oN = !oK'' su, ra
z2
+ ( r I ). 8-=-11 - -=-11 -
L- I > _=.-
oKz '[oa, oC, ) oB.oC
ozKozQ ozQ OK oQ Sou n Do vAy # > z,kd,thop vdi Vo,qsc l'o,qM N Sou N
dan tdi vo'qac ,, Q)
Vo,al,t tu
Soac
Tir (1), (2) ta nhhn duoc
/-6-r\
vo,oot.t ,AMN < l]ij l.v|ou, ldpcm).
\z )
Ding thrlc xiy ra khi vi chi khi b = c, haytam gi6c OBC vuOng cdntai O. tam gi6c OBC vuOng cdntai O.
Nhnn x6t. C6 the dirng phuong phiip luong giiic hoac
ti"n-.irii rnit phang phai giric cria'mot nhi dien de gidi
biri to6n nhy. Cric ban sau c6 ldi giii tot hon ci:
Hi N6i: DodnTri Dfing, Pham Quang Dinh, llAl'
Nhir AniTud'n.11A2, Kh6i FrfcrT, DHSP Hn Noi; Bic Ninh: Nguydn Thr)y Drortg, Nguy€n Ting. Ldm' 11
Todn,THff'chuyen
-Bic
Ninh; Hir TiryzTrinh NgocTi'
P2
= ul,P1 P1
Ngrrreir Xtdn \,'iit, I I Tohn, THPT chuy0.n Nguydn HuO;
Vinh Phric: \:ii Vritr Quottg, l2At, Ngrrylit \:drt Ngoc,
Ngrr,r,e-rr Kint Thudt. llAl, THFrf chuydn Vinh Phric,
Trtitt'li'n Plrcng, 10A2, THFT NgO Gia Tu, LAp Thach;
Hung YOn: PhatrTiirt Diittg, NgrvirtYanTho,l I Toiin,
THPT chuy6n Hung Ydn; H:ii Duorlg: l.'ir Xdn Dto,ng,