. - > ' " (
256 J
. 2) ' 1 . 2,
13
)
2731 2731 2^^ 1 048 576
Bai 37. Huang dan. Six dung tfnh cha't cua ca'p sd nhan. Tdng cac gdc cua mdt tii giac.
HStugiai. . \'
69
L u y e n t a p (tiet IO, 11)
I. MUC TIEU 1. Kie'n thufc
HS dn tap lai kien thiic 2 bai ca'p so cdng va cap so nhan
Djnh nghTa cap sd cdng, cap sd nhan, xac djnh cdng sai, cdrig bdi, sd hang ddu va so hang tdng quat cua ca'p cd cdng va tuong iing ca'p sd nhan.
Cach tfnh tdng n sd hang dSu tien . Mdt: so, tinth chat.
2. KT nang
Sau khi hgc xong bai nay HS cdn tfnh dugc cac so hang, sd hang tong quat ciia ca'p sd cdrtg va ca'p so nhan.
Giai duge mgt so dang toan ye ca'p so.
3. Thai dd
- Tu giac, tfch cue trong hgc tap.
Bie't phan biet rd cac khai niem co ban va van dung trong tiing trudng
hgp cu the. , - Tu duy cac van de ciia toan hgc itidt each Idgic va he thd'ng.
II. CHUAN BI CUA GV VA HS 1. Chuan h| ciia GV /.
• Chu^n bj cac cau hdi ggi md.
• Chuan bj pha'n mau va mdt so dd dung khac.
2. Chuan bi cua HS
• Can dn lai mdt sd kie'n thiic ba bai da hgc III. PHAN PHOI THCJI LUONG
Bai nay chia lam 2 tie't:
Tii't 1 : On tap mpt chut li thuyet vd chica cdc bdi td 38 den 40 Tii't 2 : Tii'p theo din hit.
IV. TIEN TRINH DAY HOC A. OAT VAN OE
Cau hdi 1
Xet tfnh tang giam ciia day so sau day.
a) ca'p sd cdng cd d am.
b) ca'p sd cdng cd d duong Cau hdi 2
Xel tfnh tang giam cua day sd sau day.
a) Ca'p sd nhan cd q > 1.
b) Cap sd nhan cd 0 < q < 1.
B. BAI Mdl
HOATDONCl
Bai 38. Hicdng ddn. Six dung djnh nghTa ca'p so cdng va cdp sd nhan.
HStugiai.
bdp sd .h) diing.
Bai 39. Hudng ddn. Su dung djnh nghTa cdp sd cdng, cdp sd nhan va cac"tfnh chdt ciia chiing.
Hoat ddng ciia GV Cau hdi 1
Hay xac djnh cdng thUc ve md'i quan he giiia x Va y.
Hoat ddng ciia HS Ggi y tra ldi cau hdi 1
Vi cac sd x + 6y, 5x + 2y,^x + y theo thU tu dd lap thanh mdt cdp so cdng nen 2(5x + 2y) = (x + 6y) + (8jf + y) hay x = 3y.
71
C a u hdi 2
Tii tfnh cha't cua cap sd nhan, hay tim X va y
Ggi y tra ldi cau hdi 2
Vi cac sd x^ l,^y + 2,x-3y theo thii tu dd lap thanh mdt cdp sd nhan nen (y + 2)^^ix-l)ix-3y).
The (1) vao (2), ta dugc (y + 2)^ = 0 hay y = - 2. Tir dd A: = - 6.
Bai 40. Hudng ddn. Sit dung dinh nghTa cdp sd cdng, cdp sd nhan va cac tinh chdt ciia chiing.
Hoat ddng cua G V Cau hdi 1
Hay xac dinh cdng thiic ve md'i quan he giu'a Uj, U2 va q.
Cau hdi 2
Td tinh cha't cua cap so cdng.
hay tim q.
Hoat ddng cua HS Gui y tra Idi cau hdi I
T a c d M2M3 - MjM2.^ v a M3MJ = MJM2.9 2
S u y r a M3 = Mj9 = M 2 ^ (vi MJM2 ^ 0 ) . 2
D o d d MJ = M2<7
Ggi y tra ldi cau hdi 2
Vi MJ, M2, M3 la mdt cdp sd cdng nen
MJ + M3 = 2M2.
Tu: cac ke't qua tren, suy ra
"2(9 + <? ) = 2u2 <=> q + q - 2 - 0 in 2 2 U2^0)<^q = -2iv\q^ 1).
Bai 41. Hudng ddn. Six dung dinh nghTa cap sd cdng, cdp sd nhan va cac tfnh chdt cua chiing.
Hoat ddng cua GV Cau hdi I
Cac so Mj, H2' "3 ^^^ ""'^^
khac nhau.
Cau hdi 2
Tim md'i quan he giiia Uj, U2 va q.
Cau hdi 3 Hay tfnh q.
Hoat ddng cua H S Ggi y tra Idi cau hdi I
Diing do cdp sd cdng (Mp) cd cdng sai khac 0.
Ggi y tra Idi cau hdi 2
MJ = M2<7, M3 = M2<7 v a MJ + M3 = 2 M 2 .
Ggi y tra ldi cSu hdi 3
"2(^ + <7 ) =2 2 2M2 <^ q + q -2- 0 ivi U2*0) <^ q = -2 i-vi q ^ 1).
Bai 42. Hicdng ddn. Sii dung djnh nghTa cdp sd cdng, cdp so nhan va cac tfnh chat ciia chiing.
Hoat ddng ciia GV Cau hdi 1
Ggi MJ, M2, UT, la ba so hang dau ciia cap so nhan va q la cdng bgi. MJ # 0 diing hay sai.
Cau hdi 2
Ggi d la cdng sai cua ca'p so cdng nhu bai toan. Hay tim md'i quan he giiia Uj, U2, q va d.
\
Cau hdi 3
Hay tfnh ba so hang dd.
Hoat ddng cua H S Ggi y tra Idi cau hdi 1
Diing vi neu ngugc lai thi M2 = M3 = 0,
^A A' n 148 va do do MJ + M2 + M3 = 0 ^—•- Ggi y tra Idi cau hdi 2 Til cac gia thie't ciia de bai ta cd :
"2 ~ " 1 ^ - "1 + 3c?
va M3 = M2^ = "2 + 4<i.
Suy ra M j ( ^ - l ) = 3af, U2(q - 1) = 4d.
Ggi y tra ldi cau hdi 3 HStugiai.
73
Bai 43. Huang dan. Six dung dinh nghTa cdp sd cgng, cdp sd nhan va cac tfnh chdt ciia chiing.
Hoat ddng ciia GV Cau hdi 1
Chiing minh rang day so (v^), vdi Vn = i^ji + 2, la mgt ca'p so nhan.
Cau hdi 2
Xac djnh so hang ddu va cdng bdi.
Cau hdi 3
Hay tim so hang tdng quat.
Hoat ddng cua HS Ggi y tra Idi cau hdi 1
Tii' he thdc xac dinh day sd (ô„) suy ra vdi mgi /? > 1, tacd
"n + 1 + 2 = 5(M„ + 2) hayvn+j=5v„.
Ggi y tra ldi cau hdi 2
vj = MJ + 2 = 3 va cdng bdi q - 5.
Ggi y tra Idi cau hoi 3
"n = Vn-2 = 3.5"~ - 2 .
Cau h o i v a bai tap o n t a p clciutdng III (tiet 12, 13)
I. MUC TIEU 1. Kie'n thiirc
• Phuong phap quy nap toan hgc: Ndi dung va cac budc trong phuong phap quy nap.
• Day sd, day so tang, day so giam, day so bi chan.
• Cdp sd cdng.
• Cdp so nhdn.
2. KTnang
• Bie't each chiing minh mdt day so tang, giam, day sd bi chan.
• Bie't chiing minh bai toan bang phuong phap quy nap toan hgc.
• Bie't each xac djnh mdt cdp so cdng, bie't chiing minh mdt day so la cap sd cdng.
• Bie't each xac dinh mdt cap so nhdn, chiing minh mdt day sd la cdp sd nhan.
3. Thai do
• Tu giac, tfch cue trong hgc tap. '
• Biet phan biet rd cac khai ni^m cu ban va van dung trong tiing trudng hop cu the.
- Tu duy cac vdn de ciia toan hgc mdt each Idgic va he thd'ng.
II. CHUAN BI CUA GV VA HS 1. Chu^nbiciia GV
Chudn bj cac cau hdi ggi md. • Chudn bi mdt bai kilm tra.
• Chu^n bi phdn mau, va mdt sd dd diing khac.
75
2. Chuan bj ciia HS
Cdn dn lai mdl sd kie'n thdc da hgc chuong III Lam bai kiem tra 1 tiet.
III. PHAN PHOI THCJI LUONG Bai nay chia lam 2 tie't :
Tii't 1 : On tap Tii't 2 : Kiem tra
IV. TIEN TRINH DAY HOC