Question

tìm x thuộc N,biết

a) 7 - x thuộc Ư(82) 0<7-x<hoặc=24

b) x+1 chia hết x-2

c)2x-1 thuộc B(12) và 12 <hoặc = 2x-1<hoặc = 48

1) n+5 chia hết cho n+3

c) 2n - 1 chia hết 3n + 6

Answer 1

b: \(x+1⋮x-2\)

\(\Leftrightarrow x-2+3⋮x-2\)

\(\Leftrightarrow x-2\in\left\{1;-1;3;-3\right\}\)

hay \(x\in\left\{3;1;5;-1\right\}\)

c: \(\Leftrightarrow2x-1\in\left\{12;24;36;48\right\}\)

\(\Leftrightarrow x\in\left\{\dfrac{13}{2};\dfrac{25}{2};\dfrac{37}{2};\dfrac{49}{2}\right\}\)

d: \(\Leftrightarrow n+3+2⋮n+3\)

\(\Leftrightarrow n+3\in\left\{1;-1;2;-2\right\}\)

hay \(n\in\left\{-2;-4;-1;-5\right\}\)

e: \(2n-1⋮3n+6\)

\(\Leftrightarrow6n-3⋮3n+6\)

\(\Leftrightarrow6n+12-15⋮3n+6\)

\(\Leftrightarrow3n+6\in\left\{1;-1;3;-3;5;-5;15;-15\right\}\)

hay \(n\in\left\{-\dfrac{5}{3};-\dfrac{7}{3};-1;-3;-\dfrac{1}{3};-\dfrac{11}{3};3;-7\right\}\)