exercice 2)
A = 12/5 - 3/5 x 7/9 tu dois d'abord effectuer la multiplication
A = 12/5 - [(3 x 7)/(5 x 9)] = 12/5 - 21/45 puis pour effectuer la soustraction (idem si addition) tu dois avoir le même dénominateur
A = 12/5 - 21/45 = [(12x9 )/(5x9)]-21/45 = 108/45 - 21/45 = (108-21)/45 = 87/45 = 29/15
B = (2/3 - 3) : 1/3 = [(2/3) - [(3x3)/(3x1)]] / 1/3 = (2/3 - 9/3) / 1/3 = [(2-9)/3] / 1/3 = (-7/3) / 1/3 pour diviser un quotient par un autre quotient, tu dois multiplier le premier par l'inverse du second, donc :
B = (-7/3) / 1/3 = (-7/3) x 3/1 = (-7 x 3) / (3 x 1) = -21 / 3 = -7
exercice 3)
a= (4x + x²)(-6x -3) = 24x² -12x -6x³ -3x² = -6x³ +24x² -3x² -12x = -6x³ +21x² -12x = -3x (2x² -7x +4)
b= 6x² - (x +6) - (-4x +9)(5x +8) = 6x² -x -6 -(-20x² -32x +45x +72) = 6x² -x -6 -(-20x² +13x +72) = 6x² +20x² -x -13x -6 -72 = 26x² -14x -78 = 13( 2x² -6) -14x
c= (a² +6a +4) -(a -6a² +36) + (18-a) = a² +6a +4 -a +6a² -36 +18 -a = a² +6a² +6a -a -a +4 -36 +18 = 7a² +4a -14 = 7 (a² -2) + 4a
d= (x² + 6x)(x³ -6x²) = x⁵ -6x⁴ +6x⁴ -36x³ = x⁵ -36x³ = x³ (x² -36)
