exercice 3 s'il vous plait?

A = 4/21 + 5/3
A = 4/21 + 5 x 7 / 3 x 7
A = 4/21 + 35/21
A = 39/21
a = 3 x 13 / 3 x 7
A = 13/7

B = 4/9 - 7/15
B = 4 x 5 / 9 x 5 - 7 x 3 / 15 x 3
B = 20/45 - 21/45
B = - 1/45

C = - 10/8 x - 24/15 x - 1/6
C = - 10 x - 24 x - 1/6
           8 x 15
C = 240/120 x  - 1/6
C = 240 x - 1
       120 x 6
C = - 240/ 720
C = 240 x - 1 / 240 x 3
C = - 1/3
   
D = - 12/25 : - 9/15
D = - 12/25 x - 15/9
D = - 12 x - 15
           25 x 9
D = 180/225
D = 45 x 4 / 45 x 5
D = 4/5

A = 4/21 + 5/3
A = 4/21 + 35/21
A = 39/21
A = 13/7

B = 4/9 - 7/15
B = 20/45 - 21/45
B = - 1/45

C = - 10/8 * - 24/15 * - 1/6
C= 240/120 * - 1/6
C = - 240/ 720
C = - 1/3
    
D = (- 12/25)/(- 9/15) ⇒ Diviser c'est multiplier par l'inverse.
D = - 12/25 * - 15/9
D = 180/225
D = 4/5