2.因數(shù)和倍數(shù) 解決問題

1、因數(shù)與倍數(shù),解決問題,一、復習導入，揭示課題,51,39,207,801,48,420,8976,二、探究新知,奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？,二、探究新知,奇數(shù)：5， 7， 9， 11，…偶數(shù)：8，12，20，24，…,5＋7＝12,7＋9＝16,5＋8＝13,7＋8＝15,8＋12＝20,12＋24＝36,……,……,……,奇數(shù)＋奇數(shù)＝偶數(shù),奇數(shù)＋偶數(shù)＝奇數(shù),偶數(shù)＋偶數(shù)＝偶數(shù),奇數(shù)

2、與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？,二、探究新知,奇數(shù)除以2余1,偶數(shù)除以2沒有余數(shù),奇數(shù)加偶數(shù)的和除以2還余1，所以，奇數(shù)＋偶數(shù)＝奇數(shù)。,奇數(shù)加奇數(shù)的和除以2沒有余數(shù)，所以，奇數(shù)＋奇數(shù)＝偶數(shù)。,偶數(shù)加偶數(shù)的和除以2沒有余數(shù)，所以，偶數(shù)＋偶數(shù)＝偶數(shù)。,奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？,二、探究新知,奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是

3、偶數(shù)？偶數(shù)與偶數(shù)的和呢？,偶數(shù),奇數(shù),偶數(shù),二、探究新知,奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？,所以，奇數(shù)＋偶數(shù)＝奇數(shù),,三、知識運用,三、知識運用,2. 奇數(shù)與奇數(shù)的積是奇數(shù)還是偶數(shù)？奇數(shù)與偶數(shù)的 積是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的積呢？,5×7＝35,7×9＝63,5×8＝40,7×8＝56,8×12＝96,14×24＝336