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Ebben a videóban olyan 
síkidomokról szeretnék beszélni,

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amiknek négy oldala van.

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A négy oldalú síkidomokat
a matematikában

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négyszögeknek nevezzük.

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Négyszög.

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Négy oldala van,

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ezért hívjuk négyszögnek.

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Szóval a négyszög olyan valami,
aminek négy oldala van.

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Tehát ez egy négyszög,

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ez is négyszög,

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ez is négyszög.

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Mindegyiknek négy oldala van.

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Ez is négyszög,

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és még ez is

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– még szabálytalanabbra rajzolom –,

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még ez is négyszög.

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És akkor mi nem négyszög?

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Nos, a háromszög az nem négyszög,

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három oldala van,

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1, 2, 3.

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Akkor ezt áthúzzuk.

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Az ötszögnek 5 oldala van,

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ezért nem négyszög.

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1, 2, 3, 4, 5 oldala van.

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A körnek mondhatjuk,
hogy nincs oldala,

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a kör csak egy nagy görbe,

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a kör sem lesz négyszög.

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Ha 6, 7 vagy 100 oldalú a sokszög,

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akkor az négyszög.

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Most pedig nézzük meg,

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hogy milyen speciális 
négyszögek vannak.

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Az egyik a paralelogramma.

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A paralelogramma olyan négyszög

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– ahogy egyre több matematikát
tanulsz,

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másféle megfogalmazással is 
találkozol majd –,

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a paralelogramma olyan négyszög,

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amelynek a szemközti oldalai 
párhuzamosak.

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A párhuzamos csak 
egy másik elnevezése annak,

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hogy ugyanabba az irányba mennek.

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Mit értek ez alatt?

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A paralelogramma valami ilyesmi.

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Miért?

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Azért, mert ez az oldal
szemben van ezzel az oldallal,

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és ezek ugyanabba 
az irányba mutatnak.

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Ha ide nyilakat rajzolnék,

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akkor ezek a nyilak 
ugyanarra mutatnának.

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Szóval ez a két oldal
párhuzamos,

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így mondjuk.

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És ez a két oldal
szintén párhuzamos.

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Tehát ez a paralelogramma.

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Nézzünk még más

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