Txawm tias los ntawm tsev kawm theem qis, ntau tus neeg nco qab yuav ua li cas nrhiav thaj tsam ntawm ib daim duab geometric: tsuas yog nrhiav qhov ntev ntawm txhua sab thiab nrhiav lawv cov lej. Lub perimeter yog tag nrho ntev ntawm cov ciam teb ntawm ib daim duab tiaj tus. Hauv lwm lo lus, nws yog qhov sib npaug ntawm qhov ntev ntawm nws sab. Chav tsev ntawm kev ntsuas ntawm lub perimeter yuav tsum sib npaug zos qhov ntsuas ntawm nws sab. Cov mis rau lub perimeter ntawm ib tug polygon yog P \u003d a + b + c … + n, qhov twg P yog lub perimeter, tab sis a, b, c thiab n yog qhov ntev ntawm txhua sab. Txwv tsis pub, lub voj voog (los yog ib puag ncig ntawm lub voj voog) raug xam: tus qauv p=2πr yog siv, qhov twg r yog lub vojvoog, thiab π yog tus lej tas li, kwv yees li sib npaug rau 3.14. Xav txog ob peb yam piv txwv yooj yim uas qhia kom meej tias yuav nrhiav tau qhov chaw ib puag ncig. Cia peb muab cov duab xws li square, ib daim duab plaub, daim duab peb sab, parallelogram thiab lub voj voog ua piv txwv.
Yuav ua li cas nrhiav thaj tsam ntawm ib lub square
Ib lub square yog ib lub quadrilateral uas txhua sab thiab cov ces kaum sib npaug. Txij li txhua sab ntawm ib lub square yog sib npaug, qhov sib npaug ntawm qhov ntev ntawm nws sab tuaj yeem suav nrog cov qauv P=4a, qhov twg a yog qhov ntev ntawm ib sab. Yog li, lub cheeb tsam ntawm ib lub square nrog ib sab ntawm 16.5 cm yog P \u003d 416.5 \u003d 66 cm.
Yuav ua li cas thiaj nrhiav tau ib puag ncig ntawm daim duab plaub
Ib daim duab plaub yog plaub plaub fab nrog txhua lub kaum sib npaug li 90 degrees. Nws yog lub npe hu hais tias nyob rau hauv xws li ib tug daim duab raws li ib tug duab plaub, lub lengths ntawm ob sab yog sib npaug zos ua khub. Yog tias qhov dav thiab qhov siab ntawm daim duab plaub yog tib qhov ntev, ces nws yog hu ua square. Feem ntau, qhov ntev ntawm ib daim duab plaub yog hu ua qhov loj tshaj plaws ntawm ob sab, thiab qhov dav yog qhov tsawg tshaj plaws. Yog li, txhawm rau kom tau txais qhov ib puag ncig ntawm lub duab plaub, koj yuav tsum tau muab ob npaug rau qhov sib npaug ntawm nws qhov dav thiab qhov siab: P=2(a + b), qhov twg a yog qhov siab thiab b yog qhov dav. Muab ib daim duab plaub nrog ib sab 15 cm ntev thiab lwm sab teem rau 5 cm dav, peb tau ib puag ncig sib npaug P=2(15 + 5)=40 cm.
Yuav ua li cas thiaj nrhiav tau ib puag ncig ntawm daim duab peb sab
Ib daim duab peb sab yog tsim los ntawm peb ntu uas koom nrog ntawm cov ntsiab lus (daim duab peb sab vertices) uas tsis nyob ntawm tib kab. Daim duab peb sab hu ua equilateral yog tias tag nrho peb ntawm nws sab sib npaug, thiab isosceles yog tias muaj ob sab sib npaug. Txhawm rau kom paub qhov ib puag ncig ntawm daim duab peb sab sib npaug, nws yuav tsum muab qhov ntev ntawm nws sab los ntawm 3: P \u003d 3a, qhov twg a yog ib qho ntawm nws sab. Yog tias ob sab ntawm daim duab peb sab tsis sib npaug rau ib leeg, nws yog ib qho tsim nyog yuav tsum tau ua haujlwm ntxiv: P \u003d a + b + c. Qhov ib puag ncig ntawm daim duab peb sab isosceles nrog sab 33, 33 thiab 44 feem yuav muab sib npaug rau: P=33 + 33 + 44=110 cm.
Yuav ua li cas thiaj nrhiav tau ib puag ncig ntawm parallelogram
Parallelogram yog plaub plaub fab nrog ob sab sib npaug sib npaug. Square, rhombus thiab duab plaub yogtshwj xeeb ntawm daim duab. Cov sab nraud ntawm ib qho parallelogram sib npaug, yog li ntawd, txhawm rau xam nws thaj tsam, peb siv cov qauv P \u003d 2 (a + b). Nyob rau hauv parallelogram nrog ob sab ntawm 16 cm thiab 17 cm, cov sum ntawm ob sab, los yog perimeter, yog P=2(16 + 17)=66 cm.
Yuav ua li cas thiaj nrhiav tau lub voj voog ncig
Vajvoog yog ib txoj kab kaw ncaj nraim, txhua lub ntsiab lus uas nyob ntawm qhov sib npaug ntawm qhov chaw. Lub voj voog ntawm lub voj voog thiab nws txoj kab uas hla ib txwm muaj qhov sib piv. Qhov piv txwv no qhia tau tias yog qhov tsis tu ncua, sau nrog tsab ntawv π thiab sib npaug kwv yees li 3.14159. Koj tuaj yeem paub qhov ib puag ncig ntawm lub voj voog los ntawm kev muab lub vojvoog los ntawm 2 thiab los ntawm π. Nws hloov tawm hais tias lub voj voog ntawm lub voj voog nrog ib lub vojvoog ntawm 15 cm yuav muab sib npaug rau P=23, 1415915=94, 2477
