bonjour
A = - 6/7 - 20/14
A = - 12/14 - 20 /14 = - 32/14 = - 16/7
B = 2/3 - 12/18 + 1/2
B = 12/18 - 12/18 + 9/18
B = 9/18 = 1/2
C = ( 8/4 - 4) : ( 3/4 + 1/3)
C = ( 8/4 - 16/4) : ( 9/12 + 4/12)
C = - 8 /4 x 12/13 = - 96/52 = - 24/ 13
A = 4 x - 12 + 8 x² - 5 x - 24 x + 15
A = 8 x² - 25 x + 3
A = ( x - 3 ) ( 4 + 8 x - 5 ) = ( x - 3 ) ( 8 x - 1 )