toán lp 1 ???

toán lớp 1 sao học ghê vậy lm đc cả x vs ^ luôn ô mai gi gứ chóp bạn nào lớp 1 mà giải đc bài này luôn ?????

\(\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+...+\frac{2}{21\times23}\) 

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{21}-\frac{1}{23}\)

\(=\frac{1}{3}-\frac{1}{23}\)

\(=\frac{20}{69}\)

2 / 3 x 5 + 2 / 5 x 7 + 2 / 7 x 9 + ... + 2 / 21 x 23

= 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/21 - 1/23

= 1/3 - 1/13

= 20/69

     \(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{21.23}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{21}-\frac{1}{23}\)

\(=\frac{1}{3}-\frac{1}{23}\)

\(=\frac{20}{69}\)

Dấu chấm ( . ) ở cấp 2 là dấu nhân ( x ) bn nhé

a) \(\left(8x+5\right)^2\left(4x+3\right)\left(2x+1\right)=9\)

\(\Leftrightarrow\left(64x^2+8x+25\right)\left(8x^2+10x+3\right)-9=0\)

Đặt a = \(8x^2+10x+3\)

\(\left(8a+1\right)a-9=0\)

\(\Leftrightarrow8a^2+a-9=0\)

\(\Leftrightarrow\left(a-1\right)\left(8a+9\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}a=1\\a=-\frac{9}{8}\end{cases}}\)\(\Leftrightarrow\orbr{\begin{cases}8x^2+10x+3=1\\8x^2+10x+3=-\frac{9}{8}\end{cases}}\)

mà \(8x^2+10x+3=1\Rightarrow8x^2+10x+2=0\)

\(\Rightarrow2\left(x+1\right)\left(4x+1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x=-1\\x=-0,25\end{cases}}\)

cảm ơn bạn còn mấy phần còn lại ạ

BAI 1 ; 

Bài 2: 

a, \(\dfrac{5}{23}\) \(\times\) \(\dfrac{17}{26}\) + \(\dfrac{5}{23}\) \(\times\) \(\dfrac{9}{26}\) 

= \(\dfrac{5}{23}\) \(\times\) ( \(\dfrac{17}{26}\) + \(\dfrac{9}{26}\))

= \(\dfrac{5}{23}\) \(\times\) \(\dfrac{26}{26}\)

= \(\dfrac{5}{23}\) 

b, \(\dfrac{3}{4}\) \(\times\) \(\dfrac{7}{9}\) + \(\dfrac{7}{4}\)  \(\times\) \(\dfrac{3}{9}\)

= \(\dfrac{7}{12}\) + \(\dfrac{7}{12}\)

= \(\dfrac{14}{12}\)

= \(\dfrac{7}{6}\)

1,a) \(\dfrac{17}{20}=\dfrac{51}{60};\dfrac{13}{15}=\dfrac{52}{60}\)

Làm 1,2 câu thôi nhé :(

1)

<=> 4x - 20 - 3x - 21 = 5 + 4

<=> 4x - 3x                = 5 + 4 + 20 + 21

<=>    x                      = 50

2)

<=> 20 - 5x + 7x - 14 = -2

<=>          2x              = -2 - 20 + 14

<=>          2x              = -8

<=>          x                = -8 : 2

<=>          x                = -4

Các câu sau tươg tự nha

7/9:(2+3/4x)=23/27-5/9

7/9:(2+3/4x)=8/27

      2+3/4x=7/9:8/27

      2+3/4x=21/8

          3/4x=21/8-2

          3/4x=5/8

              x=5/8:3/4

              x=5/6

\(\frac{7}{9}:\left(2+\frac{3}{4}x\right)+\frac{5}{9}=\frac{23}{27}\)

\(\Rightarrow\left(2+\frac{3}{4}x\right)+\frac{5}{9}=\frac{7}{9}:\frac{23}{27}=\frac{21}{23}\)

\(\Rightarrow2+\frac{3}{4}x=\frac{21}{23}-\frac{5}{9}=\frac{74}{207}\)

\(\Rightarrow\frac{3}{4}x=2-\frac{74}{207}=\frac{340}{207}\)

\(\Rightarrow x=\frac{340}{207}:\frac{3}{4}\)

\(\Rightarrow x=\frac{1360}{621}\)

Sr nãy nhầm >:(

\(\frac{7}{9}:\left(2+\frac{3}{4}x\right)+\frac{5}{9}=\frac{23}{27}\)

\(\Rightarrow\frac{7}{9}:\left(2+\frac{3}{4}x\right)=\frac{23}{27}-\frac{5}{9}=\frac{8}{27}\)

\(\Rightarrow2+\frac{3}{4}x=\frac{7}{9}:\frac{8}{27}=\frac{21}{8}\)

\(\Rightarrow\frac{3}{4}x=\frac{21}{8}-2=\frac{5}{8}\)

\(\Rightarrow x=\frac{5}{8}:\frac{3}{4}\)

\(\Rightarrow x=\frac{5}{6}\)

x = 5/6

7/9 : ( 2 + 3/4 x) + 5/9 = 23/27 

7/9 : ( 2 + 3/4 x) = 23/27 - 5/9 = 8/27

2 + 3/4 x= 7/9 : 8/27 = 21/8

3/4x = 21/8 - 2 = 5/8 

=> x = 5/8 : 3/4 = 5/6 

=)7/9:(2+3/4x)=8/27

=)2+3/4x=21/8

=)3/4x=5/8

=)x=5/6

a,x.3\(\dfrac{1}{4}\)+(\(\dfrac{-7}{6}\)).x-1\(\dfrac{2}{3}\)=\(\dfrac{5}{12}\)

\(\Leftrightarrow\)\(\dfrac{13}{4}\)x+(\(\dfrac{-7}{6}\))x-\(\dfrac{5}{3}\)=\(\dfrac{5}{12}\)

\(\Leftrightarrow\)\(\dfrac{13}{4}\)x+(\(\dfrac{-7}{6}\))x=\(\dfrac{25}{12}\)

\(\Leftrightarrow\)\(\dfrac{25}{12}\)x=\(\dfrac{25}{12}\)

\(\Leftrightarrow\)x=1

Vậy x=1

b,\(\dfrac{2}{5}\)+\(\dfrac{3}{5}\).(3x-3,7)=\(\dfrac{-53}{10}\)

\(\Leftrightarrow\)\(\dfrac{3}{5}\).(3x-3,7)=\(\dfrac{-53}{10}\)-\(\dfrac{2}{5}\)

\(\Leftrightarrow\)\(\dfrac{9}{5}\)x-\(\dfrac{111}{50}\)=\(\dfrac{-57}{10}\)

\(\Leftrightarrow\)\(\dfrac{9}{5}\)x=\(\dfrac{-87}{25}\)

\(\Leftrightarrow\)x=\(\dfrac{-29}{15}\)

Vậy x=\(\dfrac{-29}{15}\)

c,\(\dfrac{7}{9}\):(2+\(\dfrac{3}{4}\)x)+\(\dfrac{5}{9}\)=\(\dfrac{23}{27}\)

\(\Leftrightarrow\)\(\dfrac{7}{9}\):(2+\(\dfrac{3}{4}\)x)=\(\dfrac{8}{27}\)

\(\Leftrightarrow\)\(\dfrac{7}{18}\)+\(\dfrac{28}{27}\)x=\(\dfrac{8}{27}\)

\(\Leftrightarrow\)\(\dfrac{28}{27}\)x=\(\dfrac{-5}{54}\)

\(\Leftrightarrow\)x=\(\dfrac{-5}{56}\)

Vậy x=\(\dfrac{-5}{56}\)

a; \(\dfrac{2}{3}\)\(x\) - \(\dfrac{3}{2}\)\(x\) = \(\dfrac{5}{12}\)

    (\(\dfrac{2}{3}\) - \(\dfrac{3}{2}\))\(x\) = \(\dfrac{5}{12}\)

     - \(\dfrac{5}{6}\)\(x\) = \(\dfrac{5}{12}\)

     \(x\)   = \(\dfrac{5}{12}\) : (- \(\dfrac{5}{6}\))

     \(x=\) - \(\dfrac{1}{2}\)

Vậy \(x=-\dfrac{1}{2}\) 

b; \(\dfrac{2}{5}\) + \(\dfrac{3}{5}\).(3\(x\) - 3,7) = \(\dfrac{-53}{10}\)

           \(\dfrac{3}{5}\).(3\(x\) - 3,7) = \(\dfrac{-53}{10}\) - \(\dfrac{2}{5}\)

          \(\dfrac{3}{5}\).(3\(x\) - 3,7) = - \(\dfrac{57}{10}\)

         3\(x\) - 3,7 = - \(\dfrac{57}{10}\) : \(\dfrac{3}{5}\)

         3\(x\)   - 3,7 = - \(\dfrac{19}{2}\)

         3\(x\)         = - \(\dfrac{19}{2}\) + 3,7

          3\(x\)        = - \(\dfrac{29}{5}\)

           \(x\)         = - \(\dfrac{29}{5}\) : 3

           \(x\)        = - \(\dfrac{29}{15}\)

Vậy \(x\) \(\in\) - \(\dfrac{29}{15}\) 

c; \(\dfrac{7}{9}\) : (2 + \(\dfrac{3}{4}\)\(x\)) + \(\dfrac{5}{9}\) = \(\dfrac{23}{27}\)

    \(\dfrac{7}{9}\): (2 + \(\dfrac{3}{4}\)\(x\)) = \(\dfrac{23}{27}\) - \(\dfrac{5}{9}\)

     \(\dfrac{7}{9}\):(2 + \(\dfrac{3}{4}\)\(x\)) = \(\dfrac{8}{27}\)

      2 + \(\dfrac{3}{4}\)\(x\) = \(\dfrac{7}{9}\) : \(\dfrac{8}{27}\)

      2 + \(\dfrac{3}{4}\)\(x\) =  \(\dfrac{21}{8}\)

             \(\dfrac{3}{4}x\) = \(\dfrac{21}{8}\) - 2

             \(\dfrac{3}{4}\)\(x\) =  \(\dfrac{5}{8}\)

               \(x\) = \(\dfrac{5}{8}\) : \(\dfrac{3}{4}\)

              \(x\) =  \(\dfrac{5}{6}\)

Vậy \(x=\dfrac{5}{6}\)