Développer et réduire :
(5x - 2)² - (x - 7)(5x - 2)
= (25x² - 2(5x)(2) + 4) - (5x² -2x -35x + 14)
= 25x² -20x + 4 -5x² +2x +35x -14
= 20x² + 17x -10
Factoriser :
(5x - 2)² - (x - 7)(5x - 2)
= (5x - 2)[ (5x - 2) - (x - 7)]
= (5x - 2)(5x - 2 - x + 7)
= (5x - 2)(4x + 5)
Pour x = [tex]- \frac{5}{4} [/tex]
[ 5(-5/4) - 2 ][ 4(-5/4) + 5]
= (-25/4 - 2)(-5 + 5)
= 125/4 - 125/4 +10 -10
= 0