bonjour
a) 1/5 : ( 3/4 - 5/6) = ( 4/5 - 8) : 3
a = 1/5 : ( 9/12 - 10/12) = ( 4/5 - 40/5) : 3
a = 1/5 : - 1/12 = ( - 36/5) : 3
a = 1/5 x - 12 = -36/5 x 1/3
a - 12/5 = 36/15
a ) - 12/5 = -12/5
b) (5 : - 2/3) x ( 7/9 : 3) = ( 2 - 11/9) x ( 1 : - 2/5)
b= ( 5 x - 3/2) x ( 7/9 x 1/3) = ( 18/9 - 11/9) x ( 1 x - 5/2)
b = ( - 15 /2) x ( 7/27) = 7/9 x - 5/2
b = - 105/54 = - 35/18
b = -35/18 = - 35/18