a) 8 chia hết cho x - 1

Do \(x\in N\)=> \(x-1\ge-1\)

=> \(x-1\in\left\{-1;1;2;4;8\right\}\)

=> \(x\in\left\{0;2;3;5;9\right\}\)

b) 18 chia hết cho 2.x + 1

Do 2.x + 1 là số lẻ, \(n\in N\)nên \(2.x+1\ge1\)

=> \(2.x+1\in\left\{1;9\right\}\)

=> \(2.x\in\left\{0;8\right\}\)

=> \(x\in\left\{0;4\right\}\)