Répondre :
A=(15*4*8)/(4*7*3*15)+(5*8*3*3*4)/(3*3*3*7*5)=8/21+32/21=40/21
B=7-5/(3*5)=7-1/3=21/3-1/3=20/3
C=3/21*(13/5-(3*6)/(3*5))*3/2=3/21*(13/5-6/5)*3/2=3/21*7/5*3/2=(3*7*3)/(21*5*2)=(3*7*3)/(3*7*5*2)=3/10
B=7-5/(3*5)=7-1/3=21/3-1/3=20/3
C=3/21*(13/5-(3*6)/(3*5))*3/2=3/21*(13/5-6/5)*3/2=3/21*7/5*3/2=(3*7*3)/(21*5*2)=(3*7*3)/(3*7*5*2)=3/10