b.
đổi ra phân số
108/7-(8/9+52/7)
=108/7-8/9-52/7
=64/9

5. A = 2/1.5 + 3/5.11 + 4/11.19 + 5/19.29 + 6/29.41
A = 1/2. (1 - 1/5 + 1/5 - 1/11 + 1/11 - 1/19 + 1/19 - 1/29 + 1/29 - 1/41)
A = 1/2. (1 - 1/41) = 1/2.40//41 = 20/41
B = 1/1.4 + 2/4.10 + 3/10.19 + 4/19.31
B = 1/3. (1 - 1/4 + 1/4 - 1/10 + 1/10 - 1/19 + 1/19 - 1/31)
B = 1/3. (1 - 1/31) = 1/3. 30/31 = 10/31 = 20/62
=> 20/41 >20/62 => A > B

7/3:14/15-9/4
=7/3.15/14-9/4
=5/2-9/4
=1/4