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o i l O l i l G NANG lOi; SANG TAO CHO HOC SINH TRUNG HOG CO Sfl THDNG QOA KHAI THAC SOY LOAN LOGIC Tff CAC OAI TOAN HINH HOC PRO RfEN TRONG OAY HOC TOAN TS, PHAN A N H " Mpt trong nhdng muc tieu quan[.]
oil O l i l G NANG lOi; SANG TAO CHO HOC SINH TRUNG HOG CO Sfl THDNG QOA KHAI THAC SOY LOAN LOGIC Tff CAC OAI TOAN HINH HOC PRO RfEN TRONG OAY HOC TOAN TS, M pt nhdng muc tieu quan trpng dgy hpc loan la day eho hpe sinh (HS) biel suy nghT, biet sang tao, nghTa la hinh eho cac em kha nang caibien tri thdc, bien ddi cac ddi tupng toan hoc, lao nen san pham lu cd tlnh mdi me va cd gia In ddi vcri ban than Phai then nang luc sang tao eho HS bao ham nhieu van de, lien quan den viee trang bi kien thde eho cac em dua tren dpng CO, xue cam va tri lue, Trong pham vi bai bao nay, ehung ldi trinh bay each thuc khai thac suy luan logic ldmptsd/ja//oan/)/n/?/?oc(BTHH)phdbien dtrudng tnjng hpc casd (THCS) nhim giup HS kham pha cac BT mdi, gdp phan bdt dudng nang lue sang lao ChoHS 1, Cau true logic cua mot s o ' B T H H p h d b i e n d trudng THCS va cac djnh hudng khai thac nham thiet lap bai toan (BT) mdl CacBTHH dtrudng thong rat da dang va phong phu ve the loai, c h i n g hgn nhu: BT linh loan, BT chdng minh, BT tim cue tri htnh hpc, BT quy tich, BT dung hinh, Viec dung logic menh de de md ta chung bdi mdt cdng thdc chung la kha phdc tgp Tuy nhien, eae BTHH dupe phat bieu dudi dgng: "Chung minh menh deA => B dd: A = Pt Ap2/\ /\p„;B = q, /\q2/\ Aq„," (*) la kha phd bien tnsng chuong trinh THCS, an tarig nhieu dang loan da dan dtren Can chu y ring: chdng minh menh deA=^B nghTa la ehung minh A^B\a menh de dung Neu A la menh de sai thi hien nhien A=>B\a menh de dijng, Trong menh de A^B.A duqc gpi la gia thiet, B dupc gpi la kel luan, Cac BT dgng (') thudng cd mat saeh giao khoa, saeh bai tap; ed thd khai thac suy lugn logic tu cac BTHH phd bien dtrudng THCS de kham pha cae BT mc^ theo eae hudng sau: - Hu^g thtf nhat: [e),ngoaimuc dieh hoan ihanh ldi giai edn cdthe rut dupe ket luan (ki 1-8/2013)- PHAN A N H " B, nao nda khong? Neu cd, hay phalbieu BT: "Chung minh menh de:A => B/' Neu qua trinh suy luan chua sildung het gia Ihiet A, can chinh lai gia thiet va phat bieu cho hpp li • Wudnfir//?d'/?a/'Sddung ket qua Strong BT(*) (cd the kel hpp vdi A) de suy dien cae ketqua khae, gia sulhu dupc kel qua B^ Tudd, cho phep HS phat bieu BT: VhdngminhmenhdeA=^B^" - W[/d'/75r//ji^6a,-Nghien cuu menh deA (giathiet c u a B T O ) , datra van deed the tim dupc menh de A, cho ^ , zi> >1 la menh de dung hay khong"? Neu cd menh deA, thoa man dieu thi cdthe phat bieu BT: "Chung minh menh de: A ^^^ B" Khikhai Ihac suy luan logic theo hudng nay, HS can chij y den cac van de sau: + Oa cd /4, =? ^ la menh de dung, w'iAjt Aj nen ngoai ket quaA,=>B\a menh de dung cdn cd the lim thay nhieu dieu thu vj khac, can triet de khai thac; + Cht phat hien dupc menh deA,suydienramplsdgiathietnaoddcuaA;ehang han, =^ p^ A;72'^ Aj[j,;.s4SseC"c6 phai la menh de dung hay khong? Oe HS lra Idi duac eau hdi nay, G V ed the hudng d i n eho cac em thuc hien cae hoat dpng sau: - Lay diem P tren tia AD clio D la tnmg diem AP; gol I la tnjng diem eua AC, H la giao didm cua AM va PC [hinh 2); - Thuc hien qua trinh suy nguoc theo sa do: Dgy cho HS phuang thdc phat hien cac BT mdilampttrong nhflng each day hpc giup HSblet suy nghT.bietsangtgo Phuang thdc Chung tdlmudn GV trao ddi vdi HS khdng phai duac thuc hign mot sdm, mol ehieu ma la ca qua trinh dgy hpc, vdi mpt chudi cac hogt ddng cua ngudi hpc tuang thich vdl y dd su phgm duac l§p di lap Igi nhieu lan Qua dd, HS hinh kha nang khal thac cae BT ed "tiem nang" de phat hien BT mdi; giup HS khdng ehi sang tgo BT mdi macdn gdp phan vao viec hinh dcac 2AB = BC*-MI = MD^ AMIA = AMDA *- ZPAH = Z.CAH *~ em kha nang tu hpe, tu nghien cdu, nang dpng sang AH la trung luydn, ddng thdi la dudng eao eua tgo tn:ng hoal ddng thue tien sau • A / I P C ^ Mia trgng tam cua A^PC{c&n tgi A) (sddd suy luan nguoc da duac gian \uqc)