Ex. 17 :
a) 60=12×5 donc 17/12 = (17×5)/(12×5) = 85/60
b) 20=4×5 donc -6/5 = (-6×4)/(5×4) = -24/20
Ex. 18 :
a) 7/3 + 2/3 = (7+2)/3 = 9/3 = 3 (entier)
b) 11/4 - 5/4 = (11-5)/4 = 6/4 = 3/2 = 1,5 (décimal non entier)
c) 9/7 - 1/7 = (9-1)/7 = 8/7 = 1,142857142857...... (non décimal)
Ex. 19 :
par exemple :
a) 1 + 2/3 = 3/3 + 2/3 = 5/3
b) 1 - 3/4 = 4/4 - 3/4 = 1/4
c) 1 - 2/7 = 7/7 - 2/7 = 5/7
d) 1/3 + 3/4 = (1×4)/(3×4) + (3×3)/(4×3) = 4/12 + 9/12 = (4+9)/12 = 13/12
je te laisse finir
résultats attendus : e) -7/30
f) 37/14
Ex. 20 :
par exemple :
a) 2/3+7+1/3 = 2/3 + (7×3)/3 + 1/3 = 2/3 + 21/3 + 1/3 = (2+21+1)/3 = 24/3 = 8
b) 4/5 + 2/3 + 1/5 + 4/3 = 4/5 + 1/5 + 2/3 + 4/3
= (4+1)/5 + (2+4)/3
= 5/5 + 6/3
= 1 + 2
= 3
c) 5/4 + 1 + 7/4 = 5/4 + 4/4 + 7/4 = 16/4 = 4
tu finis ?
résultat attendu : d) 3/2
