txheem
Hauv kev tshaj tawm no, peb yuav txiav txim siab lub ntsiab lus, kev faib tawm thiab cov khoom ntawm ib qho ntawm cov duab geometric tseem ceeb - daim duab peb sab. Peb kuj tseem yuav txheeb xyuas cov piv txwv ntawm kev daws teeb meem los sib sau ua ke cov ntaub ntawv nthuav tawm.
Kev txhais ntawm daim duab peb sab
daim duab peb sab - Qhov no yog ib daim duab geometric ntawm lub dav hlau, muaj peb sab, uas yog tsim los ntawm kev sib txuas peb lub ntsiab lus uas tsis nyob ntawm ib txoj kab ncaj nraim. Ib lub cim tshwj xeeb yog siv rau kev xaiv - △.
- Cov ntsiab lus A, B thiab C yog cov vertices ntawm daim duab peb sab.
- Cov ntu AB, BC thiab AC yog ob sab ntawm daim duab peb sab, uas feem ntau txhais tau tias yog ib tsab ntawv Latin. Ej., AB = a, BC = b, THIAB = c.
- Sab hauv ntawm daim duab peb sab yog ib feem ntawm lub dav hlau bounded los ntawm ob sab ntawm daim duab peb sab.
Ob sab ntawm daim duab peb sab ntawm lub vertices tsim peb lub ces kaum, ib txwm denoted los ntawm Greek ntawv - α, β, γ thiab lwm yam vim li no, daim duab peb sab kuj hu ua polygon nrog peb fab.
Lub kaum sab xis kuj tuaj yeem txhais tau siv lub cim tshwj xeeb "∠"
- α - ∠BAC lossis ∠CAB
- β - ∠ABC lossis ∠CBA
- γ - ∠ACB lossis ∠BCA
Kev faib ua daim duab peb sab
Nyob ntawm qhov loj ntawm cov ces kaum los yog tus naj npawb ntawm qhov sib npaug, cov nram qab no cov duab yog txawv:
1. mob-angled - daim duab peb sab nrog tag nrho peb lub kaum ntse ntse, piv txwv li tsawg dua 90 °.
2. obtus Ib daim duab peb sab uas ib lub kaum sab xis siab dua 90 °. Lwm ob lub kaum sab xis yog mob.
3. lub - ib daim duab peb sab uas ib lub kaum sab xis yog, piv txwv li sib npaug 90 °. Hauv cov duab zoo li no, ob sab uas tsim lub kaum sab xis yog hu ua ob txhais ceg (AB thiab AC). Qhov thib peb sab ntawm lub kaum sab xis yog lub hypotenuse (BC).
4. ntau yam Ib daim duab peb sab uas txhua sab muaj qhov ntev sib txawv.
5. Isosceles - daim duab peb sab muaj ob sab sib npaug, uas yog hu ua lateral (AB thiab BC). Qhov thib peb yog lub hauv paus (AC). Hauv daim duab no, cov kaum sab xis yog sib npaug (∠BAC = ∠BCA).
6. Equilateral (los yog yog) Ib daim duab peb sab uas txhua sab yog tib qhov ntev. Tsis tas li ntawd, tag nrho nws cov ces kaum yog 60 °.
Daim duab peb sab Properties
1. Ib qho ntawm ob sab ntawm daim duab peb sab yog tsawg dua li ob, tab sis ntau dua qhov sib txawv. Rau kev yooj yim, peb lees txais cov qauv tsim ntawm sab - a, b и с… Tom qab ntawd:
b – c < a < b + cAt b > c
Cov cuab yeej no yog siv los kuaj kab ntu kom pom tias lawv tuaj yeem tsim ib daim duab peb sab.
2. Tus lej ntawm cov kaum sab xis ntawm ib daim duab peb sab yog 180 °. Nws ua raws los ntawm cov cuab yeej no uas nyob rau hauv daim duab peb sab obtuse ob lub ces kaum yog ib txwm mob.
3. Nyob rau hauv ib daim duab peb sab, muaj lub kaum sab xis loj dua ntawm sab loj, thiab vice versa.
Piv txwv ntawm cov dej num
Txoj Haujlwm 1
Muaj ob lub kaum sab xis paub hauv daim duab peb sab, 32 ° thiab 56 °. Nrhiav tus nqi ntawm lub kaum sab xis thib peb.
tshuaj
Wb coj cov ces kaum paub li α (32°) thiab β (56 °), thiab tsis paub - qab γ.
Raws li cov cuab yeej hais txog cov sum ntawm tag nrho cov ces kaum, ib + b + c = 180°.
Thiaj li, lub γ = 180° -a - ib = 180 ° - 32 ° - 56 ° = 92 °.
Txoj Haujlwm 2
Muab peb ntu ntawm qhov ntev 4, 8 thiab 11. Tshawb xyuas seb lawv puas tuaj yeem tsim ib daim duab peb sab.
tshuaj
Cia peb sau qhov tsis sib xws rau txhua ntu, raws li cov cuab yeej tau tham saum toj no:
11–4 <8 <11 + 4
8–4 <11 <8 + 4
11–8 <4 <11 + 8
Tag nrho cov ntawm lawv yog lawm, yog li ntawd, cov ntu no tuaj yeem yog sab ntawm daim duab peb sab.