\(\frac{3}{4}\times\frac{8}{5}\times\frac{5}{9}=\frac{3\times8\times5}{4\times5\times9}=\frac{3\times4\times2\times5}{4\times5\times3\times3}=\frac{2}{3}\)

\(\frac{3}{4}\times\frac{8}{5}\times\frac{5}{9}=\frac{3\times8\times5}{4\times5\times9}=\frac{3\times4\times2\times5}{4\times5\times3\times3}=\frac{2}{3}\)

\(2009+2009\times99\)

\(=2009\times\left(99+1\right)\)

\(=2009\times100\)

\(=200900\)

\(2009\left(99+1\right)=2009\left(100\right)=200900\)

2009+2009x99

= 2009x(1+99)

= 2009x100

= 200900

 18/11 - ( 7/11 + 3/5 )

=18/11-7/11-3/5

=1-3/5

=2/5

\(=\dfrac{0.125\cdot8\cdot25}{16\cdot0.0625\cdot45-20}=\dfrac{25}{45-20}=1\)

trả lời đi nhé sai cũng đc bừa cũng đc

để xem Hà Phương ns đúng ko
 

22,2 đúng 100%, tick nha

\(=\frac{3}{4}+\frac{6}{7}+\frac{19}{32}+\frac{1}{4}+\frac{1}{7}+\frac{13}{32}\)

\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{6}{7}+\frac{1}{7}\right)+\left(\frac{19}{32}+\frac{13}{32}\right)=1+1+1=3\)

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+....+\frac{2}{x\left(x+1\right)}=\frac{499}{999}\)

\(\Leftrightarrow\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+....+\frac{2}{x\left(x+1\right)}=\frac{499}{999}\)

\(\Leftrightarrow\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+....+\frac{2}{x\left(x+1\right)}=\frac{499}{999}\)

\(\Leftrightarrow2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{499}{999}\)

\(\Leftrightarrow\frac{1}{2}-\frac{1}{x+1}=\frac{499}{999}\div2\)

\(\Leftrightarrow\frac{1}{x+1}=\frac{1}{2}-\frac{499}{1998}\)

\(\Leftrightarrow\frac{1}{x+1}=\frac{250}{999}\)

\(\Leftrightarrow\left(x+1\right).250=999\Rightarrow x+1=\frac{999}{250}\Rightarrow x=\frac{999}{250}-1=\frac{749}{250}\)

Như kiểu đề sai hay sao ý 

\(\frac{15}{3}=15:3=5\)

\(\frac{24}{8}=24:8=3\)

\(\frac{15}{3}\)= 15 : 3 = 5

\(\frac{28}{4}\)= 28 : 4 = 7

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