Bài 5:
Đk đề bài: ` x ∈ Z `
` a) ` ` (x - 3)(2y + 1) = 7 `
` => x - 3 ; 2y + 1 ∈ Ư(7) = {±1 ; ±7} `
` => (x;y) = {(4;3) ; (10;0) ; (-2;-4) ; (-4;-1)} `
Câu b tương tự !
` c) ` ` |5x - 2| ≤ 0 `
` TH1: `
` 5x - 2 ≤ 0 `
` <=> 5x ≤ 2 `
` <=> x ≤ 2/5 ` `(ktm) `
` TH2: `
` -5x + 2 ≤ 0 `
` <=> -5x ≤ -2 `
` <=> x ≤ 2/5 ` `(ktm) `
` => x ` không tồn tại.
Bài 6:
` (x - 7)(x + 3) < 0 `
` <=> ` \(\left[ \begin{array}{l}\left \{ {{x-7>0} \atop {x+3<0}} \right. \\\left \{ {{x-7<0} \atop {x+3>0}} \right. \end{array} \right.\)
` <=> ` \(\left[ \begin{array}{l}\left \{ {{x>7} \atop {x<-3}} \right. (Vô-lý) \\\left \{ {{x<7} \atop {x>-3}} \right. \end{array} \right.\)
` <=> -3 < x < 7`