7.
( 6x - 2)² + (5x - 2)² - 4 (3x - 1 )(5x - 2)
= 36x² - 24x + 4 + 25x² - 20x + 4 - 4 ( 15x² - 5x - 6x + 2)
= 61x² - 44x + 8 - 4 (15x² - 11x + 2)
= 61x² - 44x + 8 - 60x² + 44x - 8
= x² ( r xog đề ntn đây?)
9 . ( x - 1)(x² + x + 1) - x (x + 2 )(x - 2) = 5
⇔ x³ - x² + x² - x + x - 1 - x ( x² - 4) = 5
⇔ x² - 1 - x³ +4x = 5
⇔ 4x - 1 = 5
⇔ 4x = 6
⇔ x = 3/2
Vậy x = 3/2