2,

+ n chẵn

=> n(n+5) chẵn 

=> n(n+5) chia hết cho 2

+ n lẻ

Mà 5 lẻ

=> n+5 chẵn => chia hết cho 2

=> n(n+5) chia hết cho 2

KL: n(n+5) chia hết cho 2 vơi mọi n thuộc N

MÌNH TRẢ LỜI ĐẦU TIÊN NÊN CÁC BẠN **** CHO MÌNH NHÉ

cau1 : complete the second sentence so that it has a similar meaning to the first . use the word in brackets :

1 it was a public day . all the shops were shut ( since )

=>all the shops were shut since it was a public day.

2 we did not enjoy our holiday . the weather was bad ( so )

=> the weather was bad SO we did not enjoy our holiday

3 the building has now been rebuilt . it was destroyed in the fire ( relative clause )

=>The building which was destroyed in the fire has now been rebuilt.

4 lan can not drive a car ( wish )

=>Lan wishes she could drive a car .

5 i got very wet in the rain . i had an umbrella ( although )

=>Although i had an umbrella , i got very wet in the rain.