Question

tìm x biết, (x+8) chia hết cho (x+7)

Answer 1

x + 8 = x + 7 + 1

Để x + 8 chia hết cho x + 7 thì 1 chia hết cho x + 7

x + 7 = 1 hoặc x + 7 = -1

*) x + 7 = 1

x = 1 - 7

x = -6

*) x + 7 = -1

x = -1 - 7

x = -8

Vậy x = -8; x = -6

Answer 2

\(\text{x + 8 }⋮\text{ x + 7}\)

\(\Rightarrow\) \(\text{x + 8 = x + 7 + 1}\)

mà \(\text{ x + 7 ⋮ x + 7 + 1}\)

\(\Rightarrow\) \(\text{ 7 }⋮\text{ x + 1}\)

\(\Rightarrow\) \(\text{x + 1 }\in\) \(\text{Ư( 7 )}\)

Có \(\text{Ư( 7 ) }\)\(\text{=}\) \(\left\{1;7\right\}\)

suy ra :

+) \(\text{x + 1 = 1}\) \(\Rightarrow\) \(\text{x = 0}\)

+) \(\text{x + 1 = 7}\) \(\Rightarrow\) \(\text{x = 6}\)