Elementos, perímetro e classificação.
![](https://image.jimcdn.com/app/cms/image/transf/dimension=736x10000:format=png/path/s8b09caa7cb4d0d9b/image/ibd290745ae9b0b58/version/1443142873/image.png)
Classificamos os triângulos:
![](https://image.jimcdn.com/app/cms/image/transf/dimension=645x10000:format=png/path/s8b09caa7cb4d0d9b/image/ie15dabf7385f2046/version/1443143135/image.png)
Assista ao vídeo que explica a tabela acima.https://www.youtube-nocookie.com/embed/JQPVJapETzE?wmode=transparent&vq=hd1080
Soma dos ângulos internos de um triângulo
No 7º ano verificamos experimentalmente que a soma dos ângulos internos de um triângulo é 180º.
![](https://image.jimcdn.com/app/cms/image/transf/dimension=690x10000:format=png/path/s8b09caa7cb4d0d9b/image/i5edaa4f9dfe95100/version/1443143215/image.png)
![](https://image.jimcdn.com/app/cms/image/transf/dimension=893x10000:format=png/path/s8b09caa7cb4d0d9b/image/i8b98ee8205e27143/version/1443143468/image.png)
Propriedade do ângulo externo
![](https://image.jimcdn.com/app/cms/image/transf/none/path/s8b09caa7cb4d0d9b/image/if46b1759ab9812d0/version/1443143748/image.png)