b)
7/9-1/2.7/9+1/2
=7/9-7/18+1/2
=7/18+1/2
=8/9
c)
6/7-1/2.1/3-21/6
=6/7-1/6-21/6
=29/42-21/6
=-59/21
d)
15:(-3/4)-9:(-3/4)
=-20-(-12)
=-8

a) 2/5 - (-1/3) + 1/2 - (1/3 + 2/5)
= 2/5 + 1/3 + 1/2 - 1/3 - 2/5
= (2/5 - 2/5) + (1/3-1/3) +1/2
= 0 + 0 + 1/2
=1/2
b) 7/9 - 1/2 . 7/9 +7/2
=7/9 .( 1- 1/2 + 1)
=7/9.3/2
=7/6
c)6/7 - 1/2 . 1/3 -21/6
=6/7 - 1/6 - 21/6
=6/7-11/3
=59/21
d)15:(-3/4)-9:(-3/4)
=15. (-4/3) - 9. (-4/3)
=(-4/3). (15-9)
=(-4/3).6
=-8
Cho mình 5* nhé ^^