bonsoir pouvez vous m'aider svp merci.

Bonjour,

A = 5/9 + 10/9 × 4/5
A = 5/9 + 40/45
A = 25/45 + 40/45
A = 65/45 = ( 65 ÷ 5 ) / ( 45 ÷ 5 ) = 13/9

B = 5/3 + ( 5/21 - 5/7 )
B = 5/3 + ( 5/21 - 15/21 )
B = 5/3 + -10/21
B = 35/21 + -10/21
B = -25/21

C = ( 2/9 - 3/4 ) ÷ 5/2
C = ( 8/36 - 27/36 ) ÷ 5/2
C = 19/36 ÷ 5/2
C = 19/36 × 2/5 = .../...

Je te laisse faire les deux derniers.