Question

tìm stn N cho biết 2n + 7 chia hết cho n+1

Answer 1

\(2n+7⋮n+1\)

\(\Leftrightarrow5⋮n+1\)

\(\Leftrightarrow n+1\in\left\{1;5\right\}\)

hay \(n\in\left\{0;4\right\}\)

Answer 2

\(\left(2n+7\right):\left(n+1\right)\)

= 2n : n + 2n : 1 + 7 : n + 7 : 1

= 2 + 2n : \(\dfrac{7}{n}\) + 7

= 2 + 7 + 2n . \(\dfrac{n}{7}\)
= 9 + \(\dfrac{2n^2}{7}\)

= \(\dfrac{63}{7}+\dfrac{2n^2}{7}\)

= \(\dfrac{63+2n^2}{7}\) 

(n sao mà tìm đc bn)