mik làm câu a,b,h,c,e,f
a, -3/7 + 9/7 = 6/7
b, 4/5 + 4/-18 = 4/5 + -2/9 = 36/45 + -10/45 = 26/45
h, 3/-4 - 3/7 + -1/4 = (-3/4 + -1/4) - 3/7 = -1 - 3/7 = -7/7 - 3/7 = -10/7
c, 3/5 - 5/6 = 18/30 - 25/30 = -7/30
e, 2/7 . 3/11 + 2/7 . -4/11 = 2/7 . (3/11 + -4/11) = 2/7 . -1/11 = -2/77
f, 2/5 - 1/4 + 3/10 = 8/20 - 5/20 + 6/20 = 9/20