devoir math urgent pouvais vous m'aidez au dessus svp

Bonjour,

C = 5/7 x 28/25 - (7/8 - 3/8)²
C = 140/175 - (7²/8² - 3²/8²)
C = 140/175 - (49/64 - 9/64)
C = 140/175 - 40/64
C = 140 x 64 / 175 x 64 - 40 x 175 / 64 x 175
C = 8960/11200 - 7000/11200
C = 1960/11200
C = 280 x 7 / 280 x 40
C = 7/240

D =   8/7 - 2
     1 - 1/14 : 8
D = 8/7 - 2 x 7 / 1 x 7
        1 - 1/14 x 1/8
D = 8/7 - 14/7
       1 - 1/112
D =                - 6/7_________
       1 x 112 / 1 x 112 - 1/112
D =           - 6/7_____
      112/112 - 1/112
D = - 6/7 : 111/112
D = - 6/7 x 112/111
D = - 672/777
D = 21 x - 32 / 21 x 37
D = - 32/37