1.(4.04).
rI r rl- I
" --1 = (-l)"2 =leI)'1z \/L'l' ="11_t)z =Jl=l -1 = (-l)"2 =leI)'1z \/L'l' ="11_t)z =Jl=l
Sao lai thd nhi ? Ding thrlc ndo dring ? Ding thfc nlo sai ?
(VdThdif ., bp Bl4, trudng Ngd GiaTil, Cam
NghTa, Cam Ranh, Khdnh Hda) 2.(4.04).
Gip biri toiin :
"Cho tf didn ABCD. Goi (cr) lh mat phing thay ddi luon di qua ciic trung didm / vd K ctri
cdc canh DA vit DB. Glest (cr) c6t c6rc canh CA,
CB ldn luot tai M vit N".
Nhu vay c6 phii xdt M vh N trirng v6i A vd B khong ?
Ndu cho mOt didm ndm trOn canh cta m6t tam gidc thi c5 ph6i x6t n6 tn)ng v6i hai ddu mrit
khOng ?
(Mbr hoc sinh lop 10 tadng Mac Dtnh Chi, Nam Sdch, Hdi Daong)
rnA tot - Nn7r,te sd rntr1c1.(3.04). 1.(3.04).
* Dd bei thiOu dfr kiOn, b6i bidu thrlc A v6n c6
thd nhAn gi6,tribang 33.
Vidu khi ) = 0,x= i6J =A = 33.
Dfr ki6n cdn thidu li x, y nguyOn.
* Khi th€m didu kiOn x, y nguy6n thi ldi giAi
Xr
d6 vAn chua 15 rdng... chua gi6i duoc ngoli gid rri kh6c 33 thi A nhan moi gi5 tri khdc".
(Trdn Thi Phuong Thanh, l0 Todn l, THPT
chuy€n HungY€n).
* Ndu phAn tich sd 33 nhu. trcn th) A cfrngkhong thd nhdn cdc gi6 tri 22, 55,77 ... Nhu vay khong thd nhdn cdc gi6 tri 22, 55,77 ... Nhu vay y6u cdu chrlng minh cfra dd ld sai.
Mat kh6c r, y kh6ng c6 gi6i han thu6c tap hqp
nio, tai sao phAn tich 33 thhnh tfch ci{c sd
I
nsuv€n ? Ndu 33 - ^ xllx2x33xl thi sao ?
22
(Mdt ban khdng ghi t€n).
2.(3.04):
* Goi ld bdt d8ng thrlc gifa trung binh cOng
vd trung binh nhdn ctra hai sd kh6ng Am mang tOn nhi toiin hoc ngudi Phdp C6-si (Cauchy). Thuc ra thi Oclit li ngudi chrlng minh trudc BDT ndy bang Fiinh hocl Sau d6 C*o-si dd chung minh BDT t6ng quiit cho rr s6 khdng Am.
(Nguydn Vdn Dinh, l2I, THPT Giao Thtiy, Nam Dinh).
* Lh bat ding thric Bu-nhia-c6p-ski - C6-si hay cdn goild bdt diing thtlrc vd trung binh cdng vd trung binh nhdn.
(Tr,in Thi Phaong Thanh, l0 Todn 1, THPT
chuy€n HangY€n)
3.(3.04) :
* NOn chon ciich (1). Didu ndy cfrng gi6ngnhu ban n6i "T6i c5 hai chidc brit : brit mdLu nhu ban n6i "T6i c5 hai chidc brit : brit mdLu
xanh vi brit miu d6". KhOng nOn n6i "TOi c6 hai chidc bft : bit mhu xanh holc brit mIu d6". Hay khi ban bidu di6n nghiOm dudi dang tAp
hqp nghidm thi ta c6 A = { 1 ; 21, ban s6 doc ld phdn tu cira tAp h-o,p A ln I vd2.
(Hodrrg Phfic Hung, 93, THCS Nguydn Binh Khi€m, Bidrt Hda, D6ttg Nai)
* Chon crich (1) li dring. Khi giAi thi c6 thd
n6i PT c5 2 nghiOm x = t hoic x = 2. Nhrmg khi k6t luAn thi chi chon ciich (1) md th6i.
(Dd Xudn Dftc, 88, THCS Tdn Ddn, Khodi Chdu, HangY€n).
LTS : NOu ban nho thdy c6,c cAu trA ldi tr6n chua hay, chua chdt chd thi hAy gui tidp cAu trA
ldi vd tba soan.
VKT
{iidi ddp DI Ctxuyix rHpo ToA DCI ffiab bia 4)