\(A=\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+...+\dfrac{1}{13.14}\)

\(=\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{13}-\dfrac{1}{14}\)

\(=\dfrac{1}{1}-\dfrac{1}{14}=\dfrac{13}{14}\)

Ta thấy: \(\dfrac{13}{14}< 1\)

Vậy A<1

Đặt \(A=\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+\dfrac{1}{4\cdot5}+\dfrac{1}{5\cdot6}+...+\dfrac{1}{13\cdot14}\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{13}-\dfrac{1}{14}\)

\(=1-\dfrac{1}{14}\)

\(=\dfrac{14}{14}-\dfrac{1}{14}\)

\(=\dfrac{13}{14}< 1\)

Vậy A < 1

Ta có :B= \(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+...+\dfrac{1}{13.14}\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+....+\dfrac{1}{13}-\dfrac{1}{14}\)

\(=1-\dfrac{1}{14}\)

Vì \(1-\dfrac{1}{14}< 1\)

Suy ra : \(B< 1\)

\(\frac{3}{13}+4\frac{7}{26}+1\frac{1}{12}=5+\left(\frac{3}{13}+\frac{7}{26}+\frac{1}{12}\right)=5\frac{7}{12}\)

\(\frac{2}{3}+\frac{4}{37}+5\frac{5}{11}=5+\left(\frac{2}{3}+\frac{4}{27}+\frac{5}{111}\right)\)ta thấy 2/3 > 7/12

Nên \(\frac{3}{13}+4\frac{7}{26}+1\frac{1}{2}\)< \(\frac{2}{3}+\frac{4}{37}+5\frac{5}{111}\)

\(1>\frac{2}{3}\)

\(1>\frac{3}{4}\)

\(1=\frac{5}{5}\)

\(1< \frac{9}{8}\)

\(1< \frac{12}{2}\)

\(1< \frac{14}{13}\)

\(\frac{2}{3}< 1\)

\(\frac{3}{4}< 1\)

\(\frac{5}{5}=1\)

\(\frac{9}{8}>1\)

\(\frac{12}{2}>1\)

\(\frac{14}{13}>1\)

Ủng hộ tk Đúng nhé bạn ! ^^ 

2/3<1

3/4<1

5/5=1

9/8>1

12/2>1

14/13>1

Tips:Phân số nào có tử số nhỏ hơn mẫu số thì bé hơn 1

      Phân số nào có tử số lớn hơn mẫu số thì lớn hơn 1

1 <

2 >

3 <

4 >

5 <

6 <

1)<
2)>
3)<
4)>
5)<
6)<

nhớ k mk nha

Bài 1: 

a: -8/12<0<-3/-4

b: -56/24<0<7/3

c: 4/25<1<15/13

=>-4/25>-15/13

Bài 2: 

a: =-60/45=-4/3

b: =4/15-3/2-8/5=8/30-45/30-48/30=-85/30=-17/6