Bonjour,
Exercice 2 :
b. (1/5 - 8/15) x 5/4
= ((1 x 3)/(5 x 3) - 8/15) x 5/4
= (3/15 - 8/15) x 5/4
= -5/15 x 5/4
= (-1 x 5)/(3 x 5) x 5/4
= -1/3 x 5/4
= (-1 x 5)/(3 x 4)
= -5/12
d. -4/7 ÷ (5/14 + 5/6)
= -4/7 ÷ ((5 x 3)/(14 x 3) + (5 x 7)/(6 x 7))
= -4/7 ÷ (15/42 + 35/42)
= -4/7 ÷ 50/42 diviser par un nombre, c'est multiplier par son inverse
= -4/7 x 42/50
= (-4 x 42)/(7 x 50)
= (-2 x 2 x 7 x 6)/(7 x 25 x 2)
= (-2 x 6)/25
= -12/25
