Répondre :
On donne l'expression A=(x+5)²-7x(x+5)
A = (x² +10x +25) - (7x² +35x)
A )= x² +10x +25 -7x² -35x
A = -5x² - 25x +25
2/ Factoriser A.
A = (x+5)(x+5) -7x
A = (x+5)(x+5-7x)
A = (x+5)(-6x+5)
Pour x = -2
A = (-2+5)(12+5) = 3 x 17 = 51
Pour x = 5/6
A = (5/6 +5)( -6*5/6 +5)
A = (5/6 + 30/6) ( -30/6 + 30/6)
A = 36/6 x 0 = 0
3/ Calculer A lorsque : a) x= -2 b) x=5/6 (5/6 = 5sur6)
A = (x² +10x +25) - (7x² +35x)
A )= x² +10x +25 -7x² -35x
A = -5x² - 25x +25
2/ Factoriser A.
A = (x+5)(x+5) -7x
A = (x+5)(x+5-7x)
A = (x+5)(-6x+5)
Pour x = -2
A = (-2+5)(12+5) = 3 x 17 = 51
Pour x = 5/6
A = (5/6 +5)( -6*5/6 +5)
A = (5/6 + 30/6) ( -30/6 + 30/6)
A = 36/6 x 0 = 0
3/ Calculer A lorsque : a) x= -2 b) x=5/6 (5/6 = 5sur6)