Trdn Thi Hodi Phtong, l2L, THPI Nguydn Binh
Khi6m, Bili Thi Kim Khoa, 71156A, duong Trung
Tric. khu 4, TT Trd On. VInh Long.
VU DO QUAN42 42 26 6 5 4 t l i c u lacW N G U D o N G T H I S o N N H A T H o D A P H A T D I E M P T N U T C o N S o N B C H U A D A U C H U A T H A Y T U C M A C P H U G I A Y V C N D E N V A Y I o H A B I C H D o N G N A D o S o N T A M C o C L K I E P B A C II U A T H A P TJ T C H U A M T A T H A C D A H D E N S o C o L o A B A E A C H U A K E o I P 0 U A T L A M B A L A T B C H U A C o L E H o A L U B {.1 D E N T R A N A T H U o N G T I !. C H
Gicii dap hcii :
cAcu GIAI HAY ?
(THTT só322, rhdng 4 nam 2A04)
Tru6c hdt ta nhd tai mQt kdt qu6r d(rtg sau : Trortg mdt phdng ch'o hai didm A, B vidudng
thdns @) di qua C. Khi d6 ;
a) N€u A, B cing phfa so vdi (d) thi CA + CB
dat gid tri nhd nhdt (Gf NN) khi C ld giao didm
ctia AB, vdi dudng thdns (d) (rrong đ Bt ld
giao didm d6'i xttnry voi B qua d), lilc d6
CA+CB-A8,.
b) Neu A, B khdc phia nhau so vdi (d) thi CA
+ CB dat GTNN khi C ld giao didm ctia AB voi
1d), lfic đ CA + CB = AB.
o Phdn rich sai ldm : Trong ldi gi6i đ xudt,
đ chon
^ [t. 12 €'] 2) , ,f€.1) [2 2) r]r hai didm
ctrng phia so v6i truc hohnh. Doan AB kh6ng c6t
truc Ox, tir d6 ding thfc & BDT CA + CB > AB
khOng xiy ra (khOng tdn tai didm C,, e Ox sao
cho C.rA + C,.B - AB), nghia ld CA + CB > AB.
Viy viOc k6t luAn GTNN cira him fl-r) bang .8t.6-rl
la sal lam.
2
. Khdc phuc sai ldm ; Xdt h0 truc toa dO Ory,
tren đ chon A [t f) . u, f€. - r) vd
[2 2) '[2 2)
C (x, 0). Ta c6 f(x) = CA + CB, > AB, (trong d6
M
AB, =./[q:l-.1-r-41- = .E) nen
!(2 2) [ 2 2)
> J, (Vx e R). Ding thrlc xAy ra khi
.6-f . Do d6 GTNN ctra hdm sd đ cho l} datduockhix=16 _ f .
NhAn x6t. Nhirng.ban sau c6 đp 6n tdt hon
ch : Hodrtg Vdn Tuydn, 9A, THCS Le Van Thinh, Gia Binh, Bdc Ninh ; Cuo Xtdn Nam,
GV THPT chuy6n Hd Giang, Hi Giang ; Vli
H6ng Todn, 10A, kh6i chuyen Li, DHKHTN,
DHQG Hn Noi , D6 Van Bdo, SYK47, khoa Todn - Co - Tin, DHKHTN - DHQG Hi Ndi ; L€ Vdn Lttong, 10T, THPT HI Huy TQp, TP.
Vinh, NghO An (TS xin hoan ngh6nh ban Bdo
đ dua ra mOt sO phuong rin đ giAi bhr toiin sau:
"Tim GTNN cira hdm s6
t.-
, fli ='l I +^+a +tr i + cx+a v6i di6u kien o2 - 4b< o vh 12 - 4d <0"
NGOC HI6N
GIAI PHU(,NG"TRiNH LUONT} GTrtI:
KId0NG rs6 t
Trong gid luy6n tap giii PT luong gii{c :
sinr+ cosr= tgx(l+ sirx) - 1 (l)MOt hoc sinh trong l6p đ xudt mot ldi giii MOt hoc sinh trong l6p đ xudt mot ldi giii
chi sau 5 phrit :
DK : cosx+ 0 <= x + !+kx (k e Z) 2 Dat ' r = tsl"2 = Sltlt'= . 2t l-t2 " , COSÍ= - l+t- l+tz Ex = ]t -. pf (t) tr& thhnh : - l-tt 2r ,r-t2 2t ( '' \ .r .- ,tl+11-ttoxr+tl) l+t' l+t" l-r" \ l+t' .) o (2t + I - t2)(l * t2) =.zt(l + t2 + 2t) - (1 - t4) o2t3+3t2-l=O e(r+ l)2(zt-t)=o qP*e a 1
1 (nghiOm r = *l lỏi), khi d6
l1 I
ts- =-=tscx, (dat tSg = - )
"22" " 2
)y=2a+2mx(meZ).
Ban nhan x6t nhu thd ndo vd ldi gi6i cfia hoc
sinh d6 ? Ban giAi nhu thd nho ?
NGUYEN DUC DIEP
(GV THPT Kinh MOn, Hdi Drong)
f(x)
A_
J'
Toafin hoc vid, Twil trd