A) 3\7 + 5\9 +4\7+ 4\9=(3\7+4\7) + ( 5\9 +4\9) = 7\7+9\9=63\63+63\63=126\63=42\21

b) 1\5+4\11+4\5+ 7\11=(1\5+4\5)+ (4\11+7\11)=5\5+11\11=55\55+55\55=110\55=22\11

a) \(x-\frac{4}{9}=\frac{5}{6}\)

 \(\Leftrightarrow\frac{18x}{18}-\frac{8}{18}=\frac{15}{18}\)

\(\Rightarrow18x-8=15\)

\(\Leftrightarrow18x=15+8\)

\(\Leftrightarrow18x=23\)

\(\Leftrightarrow x=\frac{23}{18}\)

Vậy \(x=\frac{23}{18}\)

b)\(x-7=\frac{1}{6}\)

\(\Leftrightarrow\frac{6x}{6}-\frac{42}{6}=\frac{1}{6}\)

\(\Rightarrow6x-42=1\)

\(\Leftrightarrow6x=42+1\)

\(\Leftrightarrow6x=43\)

\(\Leftrightarrow x=\frac{43}{6}\)

Vậy \(x=\frac{43}{6}\)

c)\(x-\frac{7}{8}=11\)

\(\Leftrightarrow\frac{8x}{8}-\frac{7}{8}=\frac{88}{8}\)

\(\Rightarrow8x-7=88\)

\(\Leftrightarrow8x=88+7\)

\(\Leftrightarrow8x=95\)

\(\Leftrightarrow x=\frac{95}{8}\)

Vậy \(x=\frac{95}{8}\)

#bn cs thể bỏ\(\Leftrightarrow;\Rightarrow\)đều đc nhé #

 #hoktot<3# 

a, x - 4/9 = 5/6 

         x   =  5/6 + 4/9

         x   =    69/54

b, x - 7 = 1/6

        x  =  1/6 + 7 

        x =  43/6

 c, x - 7/8 = 11 

          x    = 11 + 7/8 

           x   =  95/8

A) x - 4/9 = 5/6 

    x          = 5/6 + 4/9 

   x           =  23/18

 B) x - 7 = 1/6 

    x.      = 1/6 + 7 

  x.       = 43/6 

 C) x - 7/8 = 11 

    x.         = 11 + 7/8 

   x.         = 95/8

#hien#

\(A=\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+...+\frac{1}{9.11}-\frac{1}{11.13}\)

\(\Leftrightarrow A=\frac{1}{1.3}-\frac{1}{11.13}=\frac{1}{3}-\frac{1}{143}=\frac{140}{429}\)

\(A=\frac{4}{1.3.5}+\frac{4}{3.5.7}+\frac{4}{5.7.9}+\frac{4}{7.9.11}+\frac{4}{9.11.13}\)

\(\Rightarrow A=\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+...+\frac{1}{9.11}-\frac{1}{11.13}\)

\(\Rightarrow A=\frac{1}{1.3}-\frac{1}{11.13}=\frac{1}{3}-\frac{1}{143}=\frac{140}{429}\)

A =\(\frac{4}{1.3.5}+\frac{4}{3.5.7}+\frac{4}{5.7.9}+\frac{4}{7.9.11}+\frac{4}{9.11.13}\)

   = \(\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+\frac{1}{5.7}-\frac{1}{7.9}+\frac{1}{7.9}-\frac{1}{9.11}+\frac{1}{9.11}-\frac{1}{11.13}\)

   = \(\frac{1}{1.3}-\frac{1}{11.13}\)

   = \(\frac{1}{3}-\frac{1}{143}\)

  = \(\frac{140}{429}\)

Dấu "." là dấu nhân

I don"t now

Bài 1: Ta chỉ cần bỏ ngoặc rồi cộng hai phân số để ra kết quả là số tự nhiên là xong

Bài 2:

A = \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+............+\frac{1}{2003.2004}\)

A = \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-.............-\frac{1}{2003}+\frac{1}{2003}-\frac{1}{2004}\)

A = \(1-\frac{1}{2004}\)

A = \(\frac{2004}{2004}-\frac{1}{2004}=\frac{2003}{2004}\)

Mk làm mẫu 1 bài nha 

Bài 1 :

a, = (1/4+3/4) - (5/13+8/13)+2/11

    = 1 - 1 + 2/11

    = 2/11

Tk mk nha

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2003.2004}\)

\(\Leftrightarrow A=1\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2003}-\frac{1}{2004}\right)\)

\(\Leftrightarrow A=1\left(1-\frac{1}{2004}\right)\)

\(\Leftrightarrow A=\frac{2003}{2004}\)

bài 1: 

\(2\dfrac{3}{4}:1\dfrac{1}{3}=\dfrac{11}{4}:\dfrac{4}{3}=\dfrac{33}{16}\)

a, 11 + 11² + 11³ + ... + 11⁷ + 11⁸

= (11 + 11²) + (11³ + 11⁴) + ... + (11⁷ + 11⁸)

= 11(1 + 11) + 11³(1 + 11) + ... + 11⁷(1 + 11)

= 11.12 + 11³.12 + .... + 11⁷.12

= 12(11 + 11³ + ... + 11⁷) chia hết cho 12

b, 7 + 7² + 7³ + 7⁴

= (7 + 7³) + (7² + 7⁴)

= 7(1 + 7²) + 7²(1 + 7²)

= 7.50 + 7².50

= 50(7  + 7²) chia hết cho 50

c, 3 + 3² + 3³ + 3⁴ + 3⁵ + 3⁶

= (3 + 3² + 3³) + (3⁴ + 3⁵ + 3⁶)

= 3(1 + 3 + 3²) + 3⁴(1 + 3 + 3²)

= 3.13 + 3⁴.13

= 13(3 + 3⁴) chia hết cho 13

Bài 1:

a, \(\frac{1}{7}+3+\frac{5}{6}=\frac{1}{7}+\frac{3}{1}+\frac{5}{6}=\frac{6}{42}+\frac{126}{42}+\frac{35}{42}=\frac{167}{42}\)

b, \(\frac{4}{7}+\frac{5}{9}+4=\frac{4}{7}+\frac{5}{9}+\frac{4}{1}=\frac{36}{63}+\frac{35}{63}+\frac{252}{63}=\frac{323}{63}\)

A:167/42

B:692/63

Trả lời:

A . 167/42

B. 692 / 63

Hok tốt!