Tìm x biết

a) (x² – x + 7) ⋮ (x – 1);

b) (x² – 9x + 7) ⋮ (x – 9).

a) (x² – x + 7) ⋮ (x – 1)

⇔ x(x – 1) + 7 ⋮ (x – 1)

Vì x(x – 1) ⋮ (x – 1) nên 7 ⋮ (x – 1)

Suy ra x – 1 ∈ Ư(7) = {1; – 1; 7; – 7}

Do đó x ∈ {2; 0; 8; – 6}

b) (x² – 9x + 7) ⋮ (x – 9)

⇔ x(x – 9) + 7 ⋮ (x – 9)

Vì x(x – 9) ⋮ (x – 9) nên 7 ⋮ (x – 9)

Suy ra x – 9 ∈ Ư(7) = {1; – 1; 7; – 7}

Do đó x ∈ {10; 8; 16; 2}