Question

tìm số tự nhiên n biết: 2n+5⋮n+1

Answer 1

2n+5⋮n+1

vì (n+1)⋮(n+1)

=> 2(n+1)⋮(n+1)

=> (2n+2)⋮(n+1)

=> (2n+5)-(2n+2)⋮(n+1)

=> (2n+5-2n-2)⋮(n+1)

=> 3⋮(n+1)

=> (n+1)∈Ư(3){1;3}

=> n∈{0;2}

vậy n∈{0;2}

Answer 2

Giai:

2n+5⋮n+1 = 2(n+1)+3⋮n+1

⇒ n+1∈ Ư(3)⇒Ư(3)={1;3}

nếu n=3⇒n=4

n=1⇒n=2

vậy n= {4;2}