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Ta có : số chia hết cho 6 chia hết 2 và 3
Vì 2 là SNT duy nhất => các SNT >3 đều là số lẻ
=>a-1 là số chẵn=> a-1 chia hết cho 2
=>(a-1)(a+4) chia hết cho 2
Vì a>3=> a có dạng 3k+1 hoặc 3k+2
Với a có dạng 3k+1
=>a-1=3k+1-1=3k chia hết cho 3
=>(a-1)(a+4) chia hết cho 3
Với a có dạng 3k+2
=>a+4=3k+4+2=3k+6 chia hết cho 3
=>(a-1)(a+4) chia hết cho 3
Vậy chắc chắn (a-1)(a+4) chia hết cho 6
\(\Leftrightarrow\orbr{\begin{cases}x-5=0\\x+6=0\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=5\\x=-6\end{cases}}\)
\(\left(x-5\right)\left(x+6\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x-5=0\\x+6=0\end{cases}\Rightarrow\orbr{\begin{cases}x=5\\x=-6\end{cases}}}\)
1. The cake was put on the red table yesterday.
2. This hat was made for his girlfriend last Monday.
3. A lot of friends were had in Ho Chi Minh City 3 years ago.
4. He was taken to see Tri Nguyen aquarium by his uncle last week.
C tick cho e vs nhek! (E lớp 6 ak; vì cái này e hc ở Trung tâm rồi nên e giúp c nhek ak)
6 whether to tell him the truth
7 to be interested in reading book when he was small
8 we didn't live in a city with a lot of air pollution
9 she had a car
10 was reported that many people become homeless after the flood
11 is expected to pass the new law
12 and flowers in the school yard are always watered by these student everyday
13 happy to be here
14 is very exciting for her to join the group discussion
15 was pleasing that he could pass the entrance exam