Répondre :
A=((3/4)-(2/7)-2)*(21/4)
A=((21/28)-(8/28)-(56/28))*(21/4)
A=(-43/28)*(21/4)
A=-129/16
B=(-2/3)+(5/3)*(12/7)-18*(7/27)
B=(-2/3)+(5*3*4)/(3*7)-(3*6*7)/(3*9)
B=(-2/3)+(20/7)-(42/9)
B=(-42/63)+(180/63)-(126/63)
B=12/63=4/21
A=((21/28)-(8/28)-(56/28))*(21/4)
A=(-43/28)*(21/4)
A=-129/16
B=(-2/3)+(5/3)*(12/7)-18*(7/27)
B=(-2/3)+(5*3*4)/(3*7)-(3*6*7)/(3*9)
B=(-2/3)+(20/7)-(42/9)
B=(-42/63)+(180/63)-(126/63)
B=12/63=4/21