Tìm x biết: (x – 5)(x – 4) – (x + 1)(x – 2) = 7

(x – 5)(x – 4) – (x + 1)(x – 2) = 7

⇔ x² – 4x – 5x + 20 – (x² – 2x + x – 2) = 7

⇔ x² – 4x – 5x + 20 – x² + 2x – x + 2 = 7

⇔ – 8x + 22 = 7

⇔ – 8x = 7 – 22

⇔ – 8x = – 15

$\iff x=\frac{-15}{-8}$

$\iff x=\frac{15}{8}$

Vậy $x=\frac{15}{8}$ .