- Cho hpc sinh giai cdc de thi trong bd dk thi dai hpc
3.Sit dung phuang phap trirc quan, suy luan quy nap hoac dua bai toan
can giai ve cac tru'dng hgp dac biet de xet hoac dua ra cac bai toan phu mang tinh chat ggi y cho bai toan chinh.
Giai toan la qua trinh ddi hdi su tu duy nhay ben vi bai toan that da dang va phong phii. Diing trude mdt bai toan neu chua tim ra hudng di thi ngudi giai toan can phai thay ddi tu duy cua minh. Gpolya da viet trong cuon sach
" giai mdt bai toan nhu the nao" mdt cau that sau s k ; " thdnh cong trong viec
gidi bdi tap nh& vdo xdc dinh phirffng hudng chinh xdc, nh& vdo biet cdng
don dung phia". De lam dugc dieu do ngudi giai toan phai biet thir nghiem
cac mat, cac phia. Cd luc phai xet mgt vai trudng hop cu the', phai thir cac diem dac biet hoac dimg true quan h5 trg thao tac tu duy. TTiam chi co the bien ddi bai toan da cho ve bai bai toan gan gui hon, quen thugc han nhu:
- Chuyen bai toan phirc tap ve bai toan dan gian han
- Chuyin tir trudng hgp chung ve trudng hgp dac biet
- Chuyen tir trim tugng ve cu the
- Chuyen tir toan the ve bg phan
Tit ca nhCmg digu ndi tren da dugc cdng trinh kiem nghiem qua viec day hoc sinh tim ldi giai mot s6 bai toan sau day:
Bdi I: Cho tam giac ABC; Tren canh BC lay them 99 diem, ndi A vdi cac diem
' tren canh BC. Hdi cd bao nhieu tam giac tao thanh ?
Bdi 2: Cho tu giac ACBD. Hay tim each chia tir giac thanh hai tur giac co dien
tich bang nhau
Bdi 3: Cd hai thira rudng hinh chir nhat va hinh binh hanh nam canh nhau. Hay
tim each chia hai thira rudng thanh hai phan cd dien tich bang nhau ma trong
tay chi ed cuon day va hai cai egc
Bdi 4: Mgt thua rudng hinh thang cd dien tich 200 m^ Day ldn gap 3 lan day
nho. Ngudi ta chia thua rudng thanh 4 thira rugng hinh tam giac bang each cang day theo hai dudng cheo. Tinh dien tich moi phan dugc chia?
Ball- Cho tam giac ABC c6 dien tich 1200cm^. Tren canh AB ta ISy diem N
sao cho BN bSng 1/3 AB. Tren canh AC \ky dilm M sao cho AM=MC. Noi
BM va CN giao nhau tai o . Tim dien tich tam giac ABC
Bdi 6: Cho tam giac ABC, tren canh AB va AC \iy l§n Iugt hai dilm M va N
sao cho AM gap ddi BM, CN bang 1/3 AN. Hai doan thing BN va CM cat
nhau tai 0. Ndi AO keo dai cat BC tai P.
a.Tinh dien tich tam giac ABC bilt OBC bang 12 cm^
b. Xac dinh ty so hai doan thang PC va PB
Bdi 7: Cho cdc s6 tu 1 din 6 . Hay diin vdo 6 trSng tren mSr canh cua tam gidc sao cho tSr^g cdc s6 tren m6: canh bang nhar. vd tang
Bdi 8. Cho bdn dudng trdn tiep xuc nhau tai 1 dim . Tir dilm tilp xuc ke bin
dudng thang cat cac dudng trdn tai 16 diem. Hay dien cac so tir 1-17 vao cac (adsbygoogle = window.adsbygoogle || []).push({});
giao diem ciia dudng thang va dudng tron sao cho tong cac sd tren dudng tron bang 39.
Bdi 9: Mdt ba ban hang ngay that cd mgt cai can hai dia, Ba khdng tin vao can
cua minh, Ba nghi: " Ne'u can thie'u cho ngudi mua la cd tgi, cdn can thiet cho minh thi Ba khdng mudn. Ba nghi ra mgt each can nhu sau: Can sd hang cua ngudi mua lam hai ldn bang nhau:
Ldn thii nha't: Hang dat ben nay thi qua can dat ben kia
Lin thiic hai : Ba lam ngugc lai lan mdt
Hoi ba lam the ba thiet hay lgi ?
Cac bai toan d tren diu la nhimg bai toan ma hgc sinh khong phai de dang tim dugc ldi giai. Song, nhd su tac dgng cac bien phap kich thich nang
luc tu duy cho hgc sinh, cong trinh da thanh cong trong bai day thuc nghiem vdi kit qua tdt. Cdng trinh xin dugc neu va phan tich each day 2 trong 9 bai
toan ndi tren.
Cdch day bdi todn 1: Viec tim ra hudng giai quyet cua bai toan khdng he kho
khan ddi vdi hgc sinh da dugc trang bi kien thiic ve ly thuyet t6 hgp. De cac em biet van dung kien thiic da hgc vao giai quyet bai toan mgt each sang tao, giao vien chi can ggi cho hgc sinh thay dugc 101 die'm tren canh BC thang
h^ng nen khdng th^ tao thanh cac tam giac tir 101 diem dd. Vdi ggi y nay hgc
sinh de dang di d^n each giai 1: S = C^^^- (j^^ = 5050 (tam giac)
Giao vien cung cd the' ggi cho hgc sinh thay dugc mdi lien quan giua sd * tam giac vdi sd'doan thang tren canh BC de cac em di den each giai 2 :
S = C,'o, =5050(tamgiac)
Tuy nhien, hudng dan hgc sinh giai bai toan tren khi cac em chua dugc dugc trang bi kiln thirc vl ly thuylt td hgp la khd khan bdi cac em khdng the dem true tiep het dugc sd tam giac. Dieu quan trgng trong each hudng dan la phai lam cho cac em nhan tha'y :
- Mdi quan he giira sd diem them vao va phep toan tinh sd tam giac tao thanh dugc tuan theo mgt quy luat.
t . .7
Sd diem them vao
1 2 3
99
Sd tam giac tao thanh
2+1 3+2+1 4+3+2+1
100+99+98+97 +2+1
- Bie't thuc hien phep tinh mgt each sang tao roi tir do phat hien ra cong
(n + 2)(n + \)
thiic: Sn = 1+2+3+4 +n+l = ^ ^^ -
Sau khi giai xong bai toan tren, giao vien cho hgc sinh giai tiep cac bai toan
tir viec khai thae bai toan da lam dl tao ca hgi cho hoc sinh bgc 16 kha nang
sang tao: (adsbygoogle = window.adsbygoogle || []).push({});
Bai toan khai thae: Dua tren ket qua sd tam giac da tinh dugc d bai tren, yeu
B
A,
Ag9 c
Cho HS dem sd hinh chu nhat tren hinh ve (H) sau day:
Cdch day bdi todn 9
Day la mgt bai toan thuc tien vdi ngon ngir phong phu dong thdi chiia dung ham y mang tinh chat giao due. Viec hudng dSn hgc sinh tu giai dugc bai toan nay cd mgt y giao due quan trgng. No khong chi ren tu duy linh hoat trong van dung kien thiic Toan hgc vao giai quyet cac tinh hudng trong cugc sdng thuc tien ma cdn gay dugc cam giac thii vi, su to khoa hoc ciia hgc sinh,
tir do cang lam cho cac em yeu thich Toan hgc han. Viec tu tim dugc ldi giai
bai toan nay khdng phai la de dang ddi vdi hgc sinh d mgi bac hoc. Song, neu ngudi giao vien biet each din dat thi ngay chinh hgc sinh cung tu tim ra ldi giai mgt each nhe nhang .
Vdi bai toan nay, giao viSn nen sii dung phuong phap giang giai minh hoa
ket hgp phuong tien true quan ciing win dap ggi md de' giiip cho cac em co
dugc: