Bonjour
A = ab + cb
A = (2 x - 7/3) + (2/5 x - 4/7)
A = - 14/3 + ( - 8/14)
A =-196/42 - 24/42 = - 220/42 = - 110/21
B = a + b/c - d +a
B = 2 + (- 7/3 : 2/5) - 4/7 + 2
B = 2 + ( 7/3 x 5/2) - 4/7 +2
B = 2 + 35/6 - 4/7 +2
B = 21/42 + 245/42 - 24/42 + 21/42 = 263/42
C = a/b/2+1/d
C = (2 : -7/3)/2 + (1 : -4/7)
C = (2 x -3/7)/2 + (1 x -7/4)
C = (-6/7)/2 + 1 x -4/7
C = -6/7 x 1/2 + (-4/7)
C = - 6/14 - 4/7
C = 6/14 - 8/14 = -2/14 = -1/7