txheem
Cov ntsiab lus txhais
Ib daim duab plaub yog plaub plaub fab uas txhua lub kaum sab xis sib npaug. Lawv kuj ncaj thiab yog 90 °.
Lub perimeter yog qhov sib npaug ntawm qhov ntev ntawm txhua sab ntawm lub polygon. Qhov feem ntau lees txais kev xaiv yog lub peev Latin tsab ntawv P. Nyob rau hauv "P", nws yog qhov yooj yim los sau lub npe ntawm daim duab rau hauv cov ntawv me me kom tsis txhob tsis meej pem hauv txoj haujlwm ntawm txoj kev.
Yog hais tias qhov ntev ntawm ob sab yog muab nyob rau hauv txawv units, peb yuav tsis muaj peev xwm mus nrhiav tau tawm lub perimeter ntawm lub duab plaub. Yog li ntawd, rau txoj kev daws teeb meem, nws yog ib qho tsim nyog yuav tsum hloov tag nrho cov ntaub ntawv mus rau ib chav ntsuas.
Qhov ntsuas perimeter yog dab tsi?
- millimeter (hli);
- centimeter (cm);
- decimeter (dm);
- meter (m);
- kilometer (km) thiab lwm qhov ntsuas qhov ntev.
Hauv kev tshaj tawm no, peb yuav xav txog yuav ua li cas los laij qhov ib puag ncig ntawm lub duab plaub thiab txheeb xyuas cov piv txwv ntawm kev daws teeb meem.
Perimeter Formula
Lub perimeter (P) ntawm ib daim duab plaub yog sib npaug rau qhov sib npaug ntawm qhov ntev ntawm txhua sab.
P = a + b + a + b
Vim hais tias sab nraud ntawm daim duab no sib npaug, cov qauv tuaj yeem sawv cev raws li hauv qab no:
- Ob sab: P = 2*(a+b)
- Cov txiaj ntsig ntawm ob qhov txiaj ntsig ntawm sab: P = 2a+2b
Sab luv yog qhov siab / dav ntawm lub duab plaub, sab ntev yog nws lub hauv paus / ntev.
Piv txwv ntawm cov dej num
Txoj Haujlwm 1
Nrhiav ib puag ncig ntawm ib daim duab plaub yog tias nws sab yog 5 cm thiab 8 cm.
Kev txiav txim siab:
Peb hloov qhov paub qhov tseem ceeb u2bu5binto cov qauv thiab tau txais: P u8d 26 * (XNUMX cm + XNUMX cm) uXNUMXd XNUMX cm.
Txoj Haujlwm 2
Qhov ib puag ncig ntawm cov duab plaub yog 20 cm, thiab ib qho ntawm nws sab yog 4 cm. Nrhiav ob sab ntawm daim duab.
Kev txiav txim siab:
Raws li peb paub, P = 2a + 2b. Cia peb hais 4 cm yog ib sab а. Yog li tsis paub sab b, muab faib los ntawm ob, yog xam raws li hauv qab no: 2b u2d P - 20a u2d 4 cm - 12 * XNUMX cm uXNUMXd XNUMX cm.
Yog li ntawd, sab b = 12 cm / 2 = 6 cm.
Kev daws teebmeem
Thiab tam sim no xyaum!
1. Ib sab ntawm daim duab plaub yog 9cm thiab lwm qhov yog 11cm ntev. Yuav ua li cas kom paub qhov perimeter?
Peb txiav txim siab li cas:
Yog tias a = 9, ces b = 9 + 11;
Ces b = 20 cm;
Wb siv tus qauv P = 2 × (a + b);
P = 2 × (9 + 20);
lus: 58cm.
2. Nrhiav qhov ib puag ncig ntawm ib daim duab plaub nrog sab 30 mm thiab 4 cm. Qhia koj cov lus teb hauv centimeters.
Peb txiav txim siab li cas:
Hloov 30mm rau cm:
30 hli = 3 cm.
Siv tus qauv rau lub perimeter ntawm ib lub duab plaub:
P \u003d 3 + 4 + 3 + 4 \u003d 14 cm.
Teb: P = 14 cm.
3. Nrhiav qhov ib puag ncig ntawm daim duab peb sab nrog sab 2 hauv thiab 300 hli. Qhia koj cov lus teb hauv centimeters.
Peb txiav txim siab li cas:
Cia peb hloov qhov ntev ntawm sab mus rau centimeters:
2 dm = 20 cm, 300 mm = 30 cm.
Nrhiav cov perimeter siv tus qauv P = 2 × (a + b):
P \u003d 2 × (20 + 30) \u003d 2 × 50 \u003d 100 (cm).
Teb: P = 100 cm.
