Txawm cov menyuam kawm ntawv preschool paub tias daim duab peb sab zoo li cas. Tab sis nrog lawv yog dab tsi, cov txiv neej twb pib nkag siab hauv tsev kawm ntawv. Ib hom yog daim duab peb sab obtuse. Txhawm rau kom nkag siab tias nws yog dab tsi, qhov yooj yim tshaj plaws yog pom daim duab nrog nws cov duab. Thiab nyob rau hauv txoj kev xav, qhov no yog qhov lawv hu ua "qhov yooj yim tshaj plaws polygon" nrog peb sab thiab vertices, ib qho ntawm obtuse lub kaum sab xis.
Txoj kev xav
Nyob hauv geometry, muaj cov duab zoo li no nrog peb sab: acute-angled, right-angled and obtuse-angled triangles. Ntxiv mus, cov khoom ntawm cov polygons yooj yim tshaj plaws yog tib yam rau txhua tus. Yog li, rau txhua hom npe, xws li kev tsis sib xws yuav raug pom. Qhov sum ntawm qhov ntev ntawm ob sab yuav tsum tau ntau dua qhov ntev ntawm peb sab.
Tab sis txhawm rau kom paub tseeb tias peb tab tom tham txog daim duab tiav, thiab tsis yog hais txog cov txheej txheem ntawm tus kheej, koj yuav tsum tau kuaj xyuas tias qhov xwm txheej tseem ceeb tau ntsib: qhov sib npaug ntawm cov kaum sab xis ntawm daim duab peb sab obtuse yog 180o. Tib yam muaj tseeb rau lwm hom duab nrog pebtog. Muaj tseeb tiag, nyob rau hauv daim duab peb sab obtuse ib lub kaum sab xis yuav ntau tshaj 90o, thiab ob qho ntxiv yuav tsum ntse. Nyob rau hauv rooj plaub no, nws yog lub kaum sab xis loj tshaj plaws uas yuav rov qab rau sab ntev tshaj plaws. Muaj tseeb, cov no nyob deb ntawm tag nrho cov khoom ntawm daim duab peb sab obtuse. Tab sis txawm paub tsuas yog cov yam ntxwv no, cov tub ntxhais kawm tuaj yeem daws tau ntau yam teeb meem hauv geometry.
Rau txhua lub polygon nrog peb qhov vertices, nws kuj yog qhov tseeb tias los ntawm kev txuas ntxiv ntawm ib sab, peb tau txais lub kaum sab xis uas nws qhov loj me yuav sib npaug rau qhov sib npaug ntawm ob qhov tsis nyob ib sab sab hauv. Lub perimeter ntawm obtuse daim duab peb sab yog xam nyob rau hauv tib txoj kev raws li rau lwm yam duab. Nws yog sib npaug rau cov lej ntawm qhov ntev ntawm txhua sab. Txhawm rau txiav txim siab thaj tsam ntawm daim duab peb sab, cov lej suav tau muab ntau yam qauv, nyob ntawm seb cov ntaub ntawv twg pib tam sim no.
yog style
Ib qho tseem ceeb tshaj plaws rau kev daws teeb meem hauv geometry yog daim duab raug. Cov kws qhia lej feem ntau hais tias nws yuav pab tsis tau tsuas yog pom qhov tau muab thiab qhov xav tau ntawm koj li cas, tab sis kuj tau txais 80% ze dua rau cov lus teb raug. Yog li ntawd nws yog ib qho tseem ceeb kom paub yuav ua li cas los tsim ib daim duab peb sab obtuse. Yog tias koj tsuas yog xav tau ib daim duab hypothetical, ces koj tuaj yeem kos ib lub polygon nrog peb sab kom ib qho ntawm cov ces kaum siab dua 90o.
Yog tias muaj qee qhov txiaj ntsig ntawm sab ntev lossis qib ntawm cov kaum sab xis tau muab, ces nws yuav tsum tau kos daim duab peb sab obtuse-angled raws li lawv. Nyob rau tib lub sijhawm, nws yog qhov yuav tsum tau sim kom raug raws li qhov ua tauPiav cov ces kaum, xam lawv nrog ib tug protractor, thiab tso saib cov sab proportionally rau cov muab tej yam kev mob nyob rau hauv txoj hauj lwm.
Cov kab tseem ceeb
Nws feem ntau tsis txaus rau cov menyuam kawm ntawv paub tsuas yog qee cov duab yuav tsum zoo li cas. Lawv tsis tuaj yeem txwv lawv tus kheej rau cov ntaub ntawv hais txog qhov twg daim duab peb sab yog obtuse thiab uas yog lub kaum sab xis. Cov chav kawm ntawm lej tau teev tseg tias lawv txoj kev paub txog cov yam ntxwv tseem ceeb ntawm cov duab yuav tsum ua kom tiav.
Yog li, txhua tus menyuam kawm ntawv yuav tsum nkag siab lub ntsiab lus ntawm bisector, nruab nrab, perpendicular bisector thiab qhov siab. Tsis tas li ntawd xwb, nws yuav tsum paub lawv tej yam tseem ceeb.
Yog li, cov bisectors faib lub kaum sab xis hauv ib nrab, thiab sab nraud rau hauv ntu uas yog proportional rau sab uas nyob ib sab.
Qhov nruab nrab faib ib daim duab peb sab ua ob qhov sib npaug. Nyob rau ntawm qhov chaw uas lawv sib tshuam, txhua tus ntawm lawv tau muab faib ua 2 ntu hauv qhov piv ntawm 2: 1, thaum saib los ntawm sab saum toj los ntawm qhov uas nws tawm los. Nyob rau hauv cov ntaub ntawv no, qhov nruab nrab loj tshaj plaws yog ib txwm kos rau nws qhov tsawg tshaj plaws sab.
Tsis txhob mloog tsawg dua qhov siab. Qhov no yog perpendicular mus rau opposite sab ntawm lub ces kaum. Qhov siab ntawm daim duab peb sab obtuse muaj nws tus yam ntxwv. Yog hais tias nws yog kos los ntawm ib tug ntse vertex, ces nws ntog tsis nyob rau sab ntawm no yooj yim polygon, tab sis nyob rau hauv nws extension.
Lub perpendicular bisector yog ib ntu uas tawm ntawm qhov nruab nrab ntawm lub ntsej muag daim duab peb sab. Tib lub sijhawm, nws nyob ntawm lub kaum sab xis rau nws.
Ua haujlwm nrog lub voj voog
Thaum pib kawm geometry rau menyuam yausNws yog txaus kom nkag siab yuav ua li cas kos ib daim duab peb sab obtuse-angled, kawm paub qhov txawv ntawm lwm hom thiab nco ntsoov nws cov yam ntxwv yooj yim. Tab sis rau cov tub ntxhais kawm theem siab qhov kev paub no tsis txaus. Piv txwv li, ntawm qhov kev xeem, feem ntau muaj cov lus nug txog cov voj voog thiab cov ntawv sau. Thawj ntawm lawv kov tag nrho peb qhov vertices ntawm daim duab peb sab, thiab qhov thib ob muaj ib qho taw tes nrog txhua sab.
Kev tsim ib daim ntawv sau lossis ncig daim duab peb sab obtuse-angled daim duab peb sab yog qhov nyuaj dua, vim qhov no koj yuav tsum xub nrhiav seb qhov chaw nruab nrab ntawm lub voj voog thiab nws lub vojvoog yuav tsum nyob qhov twg. Los ntawm txoj kev, nyob rau hauv cov ntaub ntawv no, tsis tsuas yog ib tug cwj mem nrog ib tug pas ntsuas, tab sis kuj ib tug compass yuav dhau los ua ib tug tsim nyog cuab yeej.
Cov teeb meem tib yam tshwm sim thaum tsim cov ntawv sau ntau yam nrog peb sab. Cov kws lej tau tsim ntau yam qauv uas tso cai rau koj los txiav txim lawv qhov chaw kom raug raws li qhov ua tau.
Daim duab peb sab
Raws li tau hais ua ntej, yog lub voj voog hla tag nrho peb qhov vertices, ces qhov no hu ua lub voj voog ncig. Nws cov khoom tseem ceeb yog tias nws tsuas yog ib qho xwb. Yuav kom paub seb yuav ua li cas lub voj voog ncig ntawm daim duab peb sab obtuse yuav tsum nyob, nws yuav tsum nco ntsoov tias nws qhov chaw yog nyob ntawm qhov kev sib tshuam ntawm peb qhov nruab nrab perpendiculars uas mus rau sab ntawm daim duab. Yog hais tias nyob rau hauv ib tug mob-angled polygon nrog peb vertices qhov point no yuav nyob rau hauv nws, ces nyob rau hauv ib tug obtuse-angled polygon nws yuav nyob sab nraum nws.
Kev paub, piv txwv li, tias ib sab ntawm daim duab peb sab obtuse yog sib npaug rau nws lub vojvoog, peb tuaj yeem ua taunrhiav lub kaum sab xis uas nyob opposite lub ntsej muag paub. Nws sine yuav sib npaug rau qhov tshwm sim ntawm kev faib qhov ntev ntawm sab paub los ntawm 2R (qhov twg R yog lub vojvoog ntawm lub voj voog). Ntawd yog, kev txhaum ntawm lub kaum sab xis yuav sib npaug rau ½. Yog li lub kaum sab xis yuav yog 150o.
Yog tias koj xav pom lub vojvoog ntawm lub voj voog ncig ntawm daim duab peb sab obtuse, ces koj yuav xav tau cov ntaub ntawv hais txog qhov ntev ntawm nws sab (c, v, b) thiab nws cheeb tsam S. Tom qab tag nrho, lub vojvoog yog xam raws li nram no: (c x v x b): 4 x S. Los ntawm txoj kev, nws tsis muaj teeb meem dab tsi ntawm daim duab koj muaj: ib tug ntau yam obtuse daim duab peb sab, isosceles, txoj cai los yog mob. Nyob rau hauv txhua rooj plaub, ua tsaug rau cov qauv saum toj no, koj tuaj yeem pom thaj tsam ntawm ib qho polygon muab peb sab.
Circumscribed triangles
Tseem ntau zaus koj yuav tsum ua haujlwm nrog cov ntawv sau npe. Raws li ib tug ntawm cov qauv, lub vojvoog ntawm xws li ib tug daim duab, multiplied los ntawm ½ ntawm lub perimeter, yuav sib npaug zos ntawm daim duab peb sab. Muaj tseeb, txhawm rau pom nws, koj yuav tsum paub obtuse daim duab peb sab. Tseeb tiag, txhawm rau txiav txim siab ½ ntawm ib puag ncig, nws yuav tsum tau ntxiv lawv qhov ntev thiab faib los ntawm 2.
Yuav kom nkag siab qhov chaw nruab nrab ntawm lub voj voog uas tau sau rau hauv daim duab peb sab obtuse yuav tsum yog, koj yuav tsum kos peb lub bisectors. Cov no yog cov kab uas bisect lub ces kaum. Nws yog nyob ntawm lawv txoj kev sib tshuam uas qhov nruab nrab ntawm lub voj voog yuav nyob. Hauv qhov no, nws yuav sib npaug ntawm txhua sab.
Lub vojvoog ntawm lub voj voog uas sau rau hauv daim duab peb sab obtuse yog sib npaug rau lub hauv paus square ntawm lub quotient (p-c) x (p-v) x (p-b): p. Hauv qhov no, p yog ib nrab-ib puag ncig ntawm daim duab peb sab, c, v, b yog nws sab.
