Lub trapezoid yog plaub-tog ob sab duab nrog ob sab sib luag thiab sib txawv qhov ntev. Cov mis los laij thaj tsam ntawm tus duab plaub yog L = (b1+b2t) ie ib1 thiab b2 yog qhov ntev ntawm ob sab sib npaug thiab t yog qhov siab. Yog tias koj tsuas yog paub qhov ntev ntawm ib qho trapezoid li niaj zaus, koj tuaj yeem tsoo lub trapezoid rau hauv cov duab yooj yim thiab nrhiav qhov siab thiab ua tiav qhov suav. Thaum koj ua tiav, tsuas yog ntxiv cov chav nyob raws qhov ntev ntawm chav nyob ntawm ob sab ntawm trapezoid!
Kauj ruam
Txoj Kev 1 ntawm 2: Nrhiav Cheeb Tsam Siv Ob Sab Sab Ntev thiab Qhov Siab
Kauj Ruam 1. Ntxiv qhov ntev ntawm ob sab ua ke
Raws li lub npe cuam tshuam, ob sab sib luag yog 2 sab ntawm trapezoid uas sib luag sib luag. Yog tias koj tsis paub qhov ntev ntawm ob sab sib luag no, siv tus pas ntsuas los ntsuas lawv. Tom qab ntawd ntxiv ob qho ntxiv.
Piv txwv li, yog tias koj paub tias tus nqi ntawm sab saud sab sauv (b1) yog 8 cm thiab sab qis dua (b2) yog 13 cm, tag nrho qhov ntev ntawm ob sab sib npaug yog 8 cm + 13 cm = 21 cm (uas qhia txog ntu "b = b"1 + b2"hauv cov qauv).
Kauj Ruam 2. Ntsuas qhov siab ntawm trapezoid
Qhov siab ntawm trapezoid yog qhov nrug nruab nrab ntawm ob sab sib luag. Kos kab ib kab ntawm ob sab sib luag thiab siv tus pas ntsuas lossis lwm yam cuab yeej ntsuas los nrhiav qhov ntev ntawm kab. Sau ntawv kom koj tsis txhob hnov qab lossis poob rau lawv.
Qhov ntev ntawm hypotenuse, lossis txhais ceg ntawm trapezoid, tsis yog qhov siab ntawm trapezoid. Qhov siab kab yuav tsum yog kab rov tav rau ob sab sib luag
Kauj Ruam 3. Muab tag nrho ob sab sib npaug los ntawm qhov siab
Tom ntej no, koj yuav tsum muab tus lej sib npaug (b) thiab qhov siab (t) ntawm trapezoid. Cov lus teb yuav tsum muaj chav nyob ntawm cov chav nyob.
Hauv qhov piv txwv no, 21 cm x 7 cm = 147 cm2 uas qhia txog "(b) t" ib feem ntawm qhov kev ua zauv.
Kauj Ruam 4. Sib npaug qhov tshwm sim los txhawm rau nrhiav thaj tsam ntawm daim duab trapezoid
Koj tuaj yeem muab cov khoom saum toj no los ntawm 1/2, lossis faib los ntawm 2 txhawm rau nrhiav thaj chaw kawg ntawm trapezoid. Nco ntsoov tias cov lus teb yog nyob rau hauv cov chav nyob.
Rau qhov ua piv txwv no, thaj tsam (L) ntawm trapezoid yog 147 cm2 / 2 = 73.5 cm2.
Txoj Kev 2 ntawm 2: Xam Thaj Chaw Ntawm Trapezoid Yog Koj Paub Qhov Loj Ntawm Ib Sab
Kauj Ruam 1. Rhuav lub trapezoid rau hauv 1 lub duab plaub thiab 2 txoj cai daim duab peb sab
Kos kab ncaj los ntawm txhua lub ces kaum ntawm sab saum toj ntawm lub trapezoid perpendicular mus rau sab hauv qab. Tam sim no, daim duab trapezoid zoo li muaj 1 lub duab plaub nyob nruab nrab thiab 2 sab xis thiab sab laug peb sab. Nws yog lub tswv yim zoo los kos kab no kom koj tuaj yeem pom cov duab kom meej dua thiab suav qhov siab ntawm trapezoid.
Txoj kev no tsuas tuaj yeem siv rau tus qauv isosceles trapezoid
Kauj Ruam 2. Nrhiav qhov ntev ntawm ib qho ntawm cov hauv paus ntawm daim duab peb sab
Tshem tawm sab hauv qab ntawm trapezoid los ntawm sab saum toj. Faib qhov tshwm sim los ntawm 2 txhawm rau nrhiav qhov ntev ntawm lub hauv paus ntawm daim duab peb sab. Tam sim no koj muaj qhov ntev ntawm lub hauv paus thiab hypotenuse ntawm daim duab peb sab.
Piv txwv li, yog tias qhov ntxeev siab (b1) yog 6 cm ntev thiab sab hauv qab yog (b2) 12 cm, txhais tau tias lub hauv paus ntawm daim duab peb sab yog 3 cm (vim b = (b2 -b1)/2 thiab (12 cm - 6 cm)/2 = 6 cm uas tuaj yeem ua kom yooj yim rau 6 cm/2 = 3 cm).
Kauj Ruam 3. Siv Pythagorean txoj kev xav los nrhiav qhov siab ntawm trapezoid
Txuas qhov ntev ntawm lub hauv paus thiab hypotenuse (ntev tshaj plaws ntawm daim duab peb sab) rau hauv Pythagorean mis A2 + B.2 = C2piv txwv li A yog lub hauv paus, thiab C yog hypotenuse. Daws qhov sib npaug B txhawm rau nrhiav qhov siab ntawm trapezoid. Yog tias qhov ntev ntawm ib sab ntawm lub hauv paus yog 3 cm, thiab qhov ntev ntawm hypotenuse yog 5 cm, cov hauv qab no yog xam:
- Nkag mus rau qhov sib txawv: (3 cm)2 + B.2 = (5 hli)2
- Square tus lej: 9 cm +B.2 Luas = 25 cm
- Rho tawm txhua sab los ntawm 9 cm: B.2 Luas = 16 cm
- Nrhiav lub hauv paus square ntawm txhua sab: B = 4 cm
Lub tswv yim:
Yog tias koj tsis muaj lub xwmfab zoo meej hauv qhov kev ua zauv, yooj yim ua kom yooj yim nws ntau li ntau tau thiab tawm qhov seem raws li cov hauv paus cag, piv txwv li 32 = (16) (2) = 4√2.
Kauj Ruam 4. Plug qhov ntev ntawm ob sab sib luag thiab qhov siab ntawm trapezoid rau hauv thaj chaw mis thiab daws
Muab lub hauv paus ntev thiab qhov siab tso rau hauv cov mis L = (b1 +b2) t txhawm rau nrhiav thaj tsam ntawm trapezoid. Yooj yim cov lej kom ntau li ntau tau thiab muab cov koog sib npaug.
- Sau cov mis: L = (b1+b2) tsi
- Nkag mus rau qhov sib txawv: L = (6 cm +12 cm) (4 cm)
- Cov ntsiab lus yooj yim: L = (18 cm) (4 cm)
- Muab tus lej: L = 36 cm2.
