Salut !
Ex. 2 :
soit n le nombre recherché
a) n × 7/3 = 2 ⇒ n = 2 ÷ 7/3 = 2 × 3/7 = 6/7
donc 6/7 × 7/3 = 2
b) n × 7/3 = -5 ⇒ n = -5 ÷ 7/3 = -5 × 3/7 = -15/7
donc -15/7 × 7/3 = -5
c) n × 7/3 = 1/3 ⇒ n = 1/3 ÷ 7/3 = 1/3 × 3/7 = 3/21 = 1/7
donc 1/7 × 7/3 = 1/3
d) n × 7/3 = 28/9 ⇒ n = 28/9 ÷ 7/3 = 28/9 × 3/7 = 84/63 = (4×21)/(3×21) = 4/3
donc 4/3 × 28/9 = 7/3
Ex. 56 :
a) 3 ÷ (-3/4) = 3 × (-4/3) = -12/3 = -4
b) -9 ÷ (-1/3) = 9 × 3 = 27
c) 60/7 ÷ (-4/21) = 60/7 × (-21/4) = (60×(-21) / (7×4)
= (4×15×(-3)×7) / (7×4)
= 15 × (-3)
= -45
