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Meilleure réponse !
  • Omnes
  • Modérateur confirmé
2014-01-31T19:29:57+01:00
Salut,

Exercice 28:

A =  \frac{16}{7} *  \frac{2}{9} =  \frac{32}{63} \\
B =  \frac{40}{13} *  \frac{5}{3} =  \frac{200}{39}  \\
C =  \frac{17}{11} *  \frac{3}{10} =  \frac{51}{110} \\
D =  \frac{4}{3} *  \frac{10}{31} =  \frac{40}{93}

Exercice 31:
M =  \frac{14}{25}*  \frac{5}{7} =  \frac{70}{175} =  \frac{2}{5} \\
 N = \frac{8}{27} *  \frac{45}{16} =  \frac{360}{432} =  \frac{5}{6} \\
P =  \frac{16}{56} *  \frac{14}{9} =  \frac{224}{504} =  \frac{4}{9} \\
Q =  \frac{32}{63} *  \frac{49}{72}  =  \frac{1568}{4536} =  \frac{28}{61}

Bonne soirée !

Bonus

Exercice 31 :
On peut simplifier une partie des fractions dans un premier temps avant de les calculer:

M =  \frac{14}{25} *  \frac{5}{7} =  \frac{7*2}{5*5}  *  \frac{5*1}{7*1} =  \frac{2}{5} *  \frac{1}{1} =  \frac{2}{5} \\
N =  \frac{8}{27} *  \frac{45}{16} =  \frac{1*8}{3*9} *  \frac{5*9}{2*8} =  \frac{1}{3} *  \frac{5}{2} =  \frac{5}{6} \\
P =  \frac{16}{56} *  \frac{14}{9} =   \frac{4*4}{14*4} *   \frac{14*1}{9} =  \frac{4}{9} \\
Q =  \frac{32}{63} *  \frac{49}{72} =  \frac{4*8}{9*7} *  \frac{7*7}{9*8}  =  \frac{4}{9} *  \frac{7}{9} =  \frac{28}{81}