13/7 - 9/5 = 13x5/7x5 - 9x7/5x7 = 65/35 - 63/35 = 2/35

20/2 - 1/8 = 80/8 - 1/8 = 79/8

5/3 + 1/5 = 5x5/3x5 + 1x3/5x3 = 25/15 + 3/15 = 28/15

5/3 - 1/5 = 5x5/3x5 - 1x3/5x3 = 25/15 - 3/15 = 22/15

SORRY vì tui hông bít viết cách phân số to to như zậy

13/7-9/5=2/35

20/2-1/8=79/8

5/3+1/5=28/15

5/3-1/5=22/15

a)\(\dfrac{5}{7}+\dfrac{4}{9}=\dfrac{45}{63}+\dfrac{28}{63}=\dfrac{73}{63}\) ; \(\dfrac{9}{11}+\dfrac{3}{8}=\dfrac{72}{88}+\dfrac{33}{88}=\dfrac{105}{88}\)

\(\dfrac{4}{5}-\dfrac{2}{3}=\dfrac{12}{15}-\dfrac{10}{15}=\dfrac{2}{15}\); \(\dfrac{16}{25}-\dfrac{2}{5}=\dfrac{16}{25}-\dfrac{10}{25}=\dfrac{6}{25}\)

b)\(5+\dfrac{3}{5}=\dfrac{25}{5}+\dfrac{3}{5}=\dfrac{28}{5};10-\dfrac{9}{16}=\dfrac{160}{16}-\dfrac{9}{16}=\dfrac{151}{16}\)

\(\dfrac{2}{3}-\left(\dfrac{1}{6}+\dfrac{1}{8}\right)=\dfrac{2}{3}-\left(\dfrac{8}{48}+\dfrac{6}{48}\right)=\dfrac{2}{3}-\dfrac{14}{48}=\dfrac{32}{48}-\dfrac{14}{48}=\dfrac{3}{8}\)

a)\(\frac{2}{3}:\frac{4}{9}+\frac{1}{3}:\frac{4}{9}\)

=\(\frac{4}{9}:\left(\frac{2}{3}+\frac{1}{3}\right)\)

=\(\frac{4}{9}:1=\frac{4}{9}\)

b

a 9/4

b 49/40

c 36/35

d 144/441

    Bài 1 :

    A = 1 - 1/2 + 1/2 - 1/4 + 1/4 - 1/8 + 1/8 - 1/16 + ... + 1/32 - 1/64

    A = 1 - 1/64

    A = 63/64

a Đ

b S

c S

d Đ

a ) S 

b ) Đ

c ) S

d ) Đ

k cho mk nhé 

Ta có: 272727x28 - 282828x27 = 27x10101x28 - 28x10101x27 = 0

Vậy, phép tính đã cho bằng 0

4) \(\frac{29x101-101}{2x19x101+4x101}\)

= \(\frac{\left(29-1\right)x101}{\left(38-4\right)x101}\)

=\(\frac{28}{34}=\frac{14}{17}\)

5) \(\left(\frac{2}{7}+\frac{11}{7}+\frac{1}{7}\right)-\frac{3}{8}-\frac{5}{8}+\frac{1}{3}\)

= \(\frac{14}{7}-\frac{8}{8}+\frac{1}{3}\)

= \(2-1+\frac{1}{3}=\frac{4}{3}\)

Nhớ tk cho mình nhé

1\(\frac{423133x846267+423134}{423133x846267+423134}=1\))

\(\frac{\left(423133+1\right)x846267-423133}{423133x846267+423134}\)

=\(\frac{423133x846267+846267-423133}{423133x846267+423134}\)

= \(\frac{423133x846267+423134}{423133x846267+423134}\)

= 1

Nhớ tk cho mình nhé (các câu sau  làm riêng cho đỡ dài

=1-\(\frac{1}{2}\)+1/3-1/4+...+1/8-1/9

=1-1/9

=8/9

\(S=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\)

\(S=1-\frac{1}{9}=\frac{8}{9}\)

kết quả = \(\frac{269}{210}\)nha bạn

ai tốt bụng thì tk cho mk , mk đg âm điểm đây huhu

=793/630 

phải ko