L EF Vi ,4, I MN ndn MNllEF TU d
Ta thdy di6n tich fl#,E n= !g14g114p1=
- Bei erai dd cho d6p ,8so sai m > I t Nguv6n
nhAn dAn ddn sai 1Am ld vi6c nhAn x6t
"PT 12 + (x+1;2 = , * (\)
c6 nghiAm
x" +x+L
duy nhdt khi PT 2t2 -t = tt1. (2) c6 nghiAm duy
nhdtuoit>?ftl".
4
rto rang neu co mdt gi6 tri cri.a r mi t > I
4
thi theo c6ch ddt t = x2 + r * 1 tridng iing sE
c6 hai g16 tri cria r th6a m6n ring bu6c d6,
dAn ddn PT ban ddu kh6ng thd c6 nghi6m duy nhdt dr.roc.
Od *r6c phuc sai ldm ta phAi tnem aiO:u
ki6n PT (dn r): x2+x+(1-t) = 0 c6 nghiOm duy nhdt, khi d6 phiii c6 bi6t thrlc A = 1-4(1- f) = 0
o1
a t - 9, lric d6 r = -= U nghiOm duy nhdt
42-
cria PT (1) vd rn = I U g16 tri cAn tim.
8
M6t sd ban giAi lai bdi to6n bdng cdch *it
didu kiQn cd,n ud. di sau khi da nhAn x6t ring
PT (1) c6 nghiOm x = x6t thi n6 ctrng nhAn
x = (-l - r) lim nghi6m, cirng di ddn d6p sd
dring. C6c ban sau c6 d6p.6n tdt hon cA :
Nguydn Mq,nh Htng,98, THCS Tr) Son,
Tit Son, Bic Ninh, NguydnVd.n Hdu,l1Al,
THPT Y6n Dirng II, Y6n D[ng, Bic Giang ;
LA C6ng Tvuydn, 11A1, THPT chuy6n Vinh
Phfc, Vinh Phric , Nguydn Dinh T|tdn,11PT3, THPT Nguy6n Hu6, Hd Tdy ; LA Thi 11PT3, THPT Nguy6n Hu6, Hd Tdy ; LA Thi
Ttdng, 1181, THPT Hohng H5a II, Hoing
H6a' Thanh H6a'
NGoc HIdN
co HqP r,i xuoNc r
Gqp bni to6n"Cho tam gidc ABC uudng tai
A, AC = b, AB = c. M td mdt didm ffAn canh
BC. Goi E ud, F ldn ltqt ld tdm dtdng trdn
ngog,i tidp tam gidc ABM ud. tatn gid,c ACM. Xdc dinh ui tri cia m ad d4n tich lAEF nh6
nhdt. Tinh gid, tri nh6 nhdt d6 theo b, c" c6
m6t ban da gtai nhu sau :
DtnsAH LBC (H e Bq.
Ta c6 ffifu=2ffifu , frfu=zfrfu,
"uy ru ffifu*ffifu = 2(ffifu+frb = 180o.
* frfri=EfrF = 9oo, do d6 ttt g)hc AEMF
nQi tidp trong drrdng trdn dudng kinh EF.
Ta thdy di6n tich fl#,En = !g14g114p1=2 2
lnt.nr 4 >!eu, 4 > !ta, =I(-tt_)4 Alb'+c')
D&ng thrlc x6y ra <+ M trtng v6i H. Do d6