Question

1.Tìm x:a) 3x - (5-17) =2x +7

b) 10 -(5-x)=30 +(2x-3)

2 .Tìm n là số tự nhiên, biết :

a) 15:(n-2)

b) (n - 2): n +1

c) 5 n+3:n+1

đ)n²+ n+7:n+1

Chú ý: là chia hết nhé!!!!!!!

Giúp tui nha!!!!!!!!

Answer 1

Bài 1:

a) \(3x-\left(5-17\right)=2x+7\)

\(\Rightarrow3x+12=2x+7\)

\(\Rightarrow x+5=0\)

\(\Rightarrow x=-5\)

Vậy \(x=-5\)

b) \(10-\left(5-x\right)=30+\left(2x-3\right)\)

\(\Rightarrow10-5+x=30+2x-3\)

\(\Rightarrow5+x=27+2x\)

\(\Rightarrow x+22=0\)

\(\Rightarrow x=-22\)

Vậy \(x=-22\)

Answer 2

Bài 2:

Giải:
a) Ta có: \(15⋮n-2\)

\(\Rightarrow n-2\in\left\{-1;1;-15;15\right\}\)

+) \(n-2=-1\Rightarrow n=1\)

+) \(n-2=1\Rightarrow n=3\)

+) \(n-2=-15\Rightarrow n=-13\)

+) \(n-2=15\Rightarrow n=17\)

Vậy \(n\in\left\{1;3;-13;-17\right\}\)

b) Ta có: \(n-2⋮n+1\)

\(\Rightarrow\left(n+1\right)-3⋮n+1\)

\(\Rightarrow3⋮n+1\)

\(\Rightarrow n+1\in\left\{1;-1;3;-3\right\}\)

+) \(n+1=1\Rightarrow n=0\)

+) \(n+1=-1\Rightarrow n=-2\)

+) \(n+1=3\Rightarrow n=2\)

+) \(n+1=-3\Rightarrow n=-4\)

Vậy \(n\in\left\{0;2;-2;-4\right\}\)

c) Ta có: \(5n+3⋮n+1\)

\(\Rightarrow\left(5n+5\right)-2⋮n+1\)

\(\Rightarrow5\left(n+1\right)-2⋮n+1\)

\(\Rightarrow2⋮n+1\)

\(\Rightarrow n+1\in\left\{1;-1;2;-2\right\}\)

+) \(n+1=1\Rightarrow n=0\)

+) \(n+1=-1\Rightarrow n=-2\)

+) \(n+1=2\Rightarrow n=1\)

+) \(n+1=-2\Rightarrow n=-3\)

Vậy \(n\in\left\{0;-2;1;-3\right\}\)

d) Ta có: \(n^2+n+7⋮n+1\)

\(\Rightarrow n\left(n+1\right)+7⋮n+1\)

\(\Rightarrow7⋮n+1\)

\(\Rightarrow n+1\in\left\{1;-1;7;-7\right\}\)

+) \(n+1=1\Rightarrow n=0\) ( t/m )

+) \(n+1=-1\Rightarrow n=-2\) ( t/m )

+) \(n+1=7\Rightarrow n=6\) ( t/m )

+) \(n+1=-7\Rightarrow n=-8\) ( không t/m )

Vậy \(n\in\left\{0;-2;6\right\}\)