Bqn Hodng Thanh Ha, ldp 83,
THCS Qudng Ninh,
Qudng Trqch, Qudng Blnh t6m sr.t:
Ttt nhd em dd khao khdt sau ndy l6n l6n ldm bdc si. Ba thudng n6i dtta :
'con muSn thdnh bdc siiuong taitht
,{l,*$,
phdi chtu bQnh cho cdc bdi todn ngay fi bdy
gid'.,Th6 ld cO hAng thdng ery ryua bdo vO
nghiiln ngAm... md em thfch nhAt vdn ld chuydn
muc "Sai l*m 0 dAu ?'.
bi t Cau n6i c0a ba HA sao rnA tnJng ! c0a
KlHlVl <r6n th6 I Vfy thi di6u ddng sg hh cdc
bdc si phAi tr6nh lA-gi nhi ? Chdn dodn nhim bQnh hay kO don sai ?
nAu n6t qdc b6c sT tuong lai d6u thdy ring :
N6u c6 ddm M 0 ngoAi B, C ben ndy thl sE
khdng c6 v! trf tht hai & ngodi bdn kia !
pdi n6u the thi ... dinh A vA hai didm M ndy s6 thEng hAng m6t !
Dic biQt khi tam gidc ABC cdn t4i A thi kh6ng
c6 did;n M nio d ngoAi B, C th6a mdn bdi todn.
MQt s0 bqn cdn tinh hon khi chi ra M c6 2 vi trf d
b6n trong cqnh BC.
Cdc bqn d6 sr] dr,rng phuong tich ttr M^dOn dudng tr0n (Q ngoqi ti6p tam gidc ABC dd gi6i
dUng bAi todn :
+.NOu M d ngoAi B, C thi M ld; giao c0a ti6p
tuyOn tai A cia duUng trdn ngo4itiCp (C) vdi BC,-
+ NOu M d trong doqn 8C thi M la giao c0a
duOtng tldn dudng kinh OA, (O lA tdm dudn$ trdn
ngoqiti6p (Q)vd BC.
Nhu vQy : N6u tam gidc. ABC cdn tqi A thl c6 2\ vi tri cOa Mth6a mdn. NOu tam gi6c ABC khOng
cdn dinh A thi c6 3 vi tric0a Mth6a mdn :
Ri6ng KlHlVl nghT nlai ... tqi sao tdg giA lai
nhdm li6n ti6p d6n th6 ? Ri6ng hai d6ng thtld
BM., = AMrvd AMr= CMrcong chi d.Ung khi 4,
Mr U lrong do4n BC. (lHlVl-c0ng th6t vgng nhu
ban V0 HAi Son vd ldn thdn dodn : Hay lA ...
sdch in sai ?
7-u quri
Y-=\ 59 \SA9
l'a thir ntt i vt)ng trdn trOn hinh sao thu0c dfng I hing. Gii s* tdng c6c sdtrOn m6i htrng
lin luvt la r;. -,- l. a+2, a+3, a+4 th\
a + (ci+ 1,-,.r-l) + (a+3) + (a+4)
= 2t0-1-l--1*-1+-5+6+7+8+9) = 90