cách này mình tự nghĩ 

\(\hept{\begin{cases}A=\frac{4}{7}+5+\frac{3}{7^2}+\frac{5}{7^3}+\frac{6}{7^4}\\B=\frac{5}{7^4}+5+\frac{6}{7^2}+\frac{4}{7}+\frac{5}{7^3}\end{cases}}\)

\(\Rightarrow A-B=\left(\frac{4}{7}-\frac{4}{7}\right)+\left(\frac{5}{7^3}-\frac{5}{7^3}\right)+\left(5-5\right)+\left(\frac{3}{7^2}-\frac{6}{7^2}\right)+\left(\frac{6}{7^4}-\frac{5}{7^4}\right)\)

\(\Rightarrow A-B=-\frac{3}{7^2}+\frac{1}{7^4}\)

\(\Rightarrow A-B=\frac{-3\times7^2}{7^4}+\frac{1}{7^4}\)

mà \(-3\times7^2< 1\Rightarrow\frac{1}{7^4}>\frac{-3\times7^2}{7^4}\Rightarrow B>A\)

giúp nhanh ạ, mình cần gấp

Bài 5:

a: =1/3+2/5

=5/15+6/15

=11/15

b: =6/21+12/21=18/21=6/7

c: =16/24+10/24

=26/24

=13/12

d: =4/12+3/12+10/12

=17/12

e: =19/24-9/24

=10/24

=5/12

f: =8/9-3/9=5/9

g: =9/3+1/3=10/3

k: =15/24+42/24+14/24

=71/24

1. A - B = 40+ 3/8 + 7/8² + 5/8³ + 32/8^{5 -} (24/8² + 40+ 5/8² + 40/8⁴ + 5/8^{4 )}

⁼ 40.8⁵/8⁵ + 3.8⁴/8⁵ + 7.8³/8⁵ + 5.8²/8⁵ + 32/8⁵ - 24.8³/8⁵ - 40.8⁵/8⁵ - 5.8³/8⁵ - 40.8/8⁵ - 5.8/8⁵

⁼ 40.8⁵/8⁵ + 24.8³/8⁵ + 7.8³/8⁵ + 5.8²/8⁵ + 32/8⁵ - 24.8³/8⁵ - 40.8⁵/8⁵ - 5.8³/8⁵ - 40.8/8⁵ - 5.8/8⁵

⁼ 7.8³/8⁵ + 5.8²/8⁵ + 32/8⁵ - 5.8³/8⁵ - 40.8/8⁵ - 5.8/8⁵

⁼ 7.8³/8⁵ + 5.8²/8⁵ -8/8⁵ - 5.8³/8⁵ - 40.8/8⁵

= 2.8³/8⁵ + 5.8²/8⁵ - 40.8/8⁵ - 8/8⁵

= 2.8³/8⁵ + 40.8/8⁵ - 40.8/8⁵ - 8/8⁵

= 2.8³/8⁵  - 8/8⁵ > 0 

Vay A > B

ai so sanh C va D di ma duoc thi minh se tink cho