Bài 2: 

a) \(\frac{x}{-27}=\frac{-3}{x}\Leftrightarrow-\frac{x}{27}=-\frac{3}{x}\Leftrightarrow-x.x=\left(-27\right).\left(-3\right)\Leftrightarrow-x^2=-81\Leftrightarrow\orbr{\begin{cases}x=9\\x=-9\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=9\\x=-9\end{cases}}\)

b) \(\frac{-9}{x}=\frac{-x}{\frac{4}{49}}\Leftrightarrow-\frac{9}{x}=-\frac{49x}{4}\Leftrightarrow-9.4=-x.49x\Leftrightarrow-36=-49x^2\Leftrightarrow\orbr{\begin{cases}x=\frac{6}{7}\\x=-\frac{6}{7}\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{6}{7}\\x=-\frac{6}{7}\end{cases}}\)

\(\frac{-9}{x}=\frac{-x}{\frac{4}{49}}\)

=> \(x\left(-x\right)=\left(-9\right)\frac{4}{49}\)

=> \(-x^2\)\(=\frac{-36}{49}\)

=> \(x^2=\frac{36}{49}\)

=> \(x=\frac{6}{7}\)

\(\frac{-9}{x}=\frac{-x}{\frac{4}{49}}\)

\(\Rightarrow x^2=\left(-9\right)\left(\frac{-4}{49}\right)\)

\(\Rightarrow x^2=\frac{36}{49}\)

\(\Rightarrow x=\sqrt{\frac{36}{49}}\)

\(\Rightarrow x=\frac{\sqrt{36}}{\sqrt{49}}\)

\(\Rightarrow x=\frac{\sqrt{6^2}}{\sqrt{7^2}}\)

\(\Rightarrow x=\frac{6}{7}\)

vay \(x=\frac{6}{7}\)

\(\Leftrightarrow x^2=9\times\frac{4}{49}\)

\(\Leftrightarrow x^2=\frac{36}{49}\)

\(\Leftrightarrow x^2=\left(\frac{3}{7}\right)^2\)

\(\Rightarrow x=\frac{3}{7}\)

a) \(x-\frac{10}{3}=\frac{7}{15}\cdot\frac{3}{5}\)                          b) \(x+\frac{3}{22}=\frac{27}{121}\cdot\frac{11}{9}\)

\(\Leftrightarrow x-\frac{10}{3}=\frac{7}{25}\)                                \(\Leftrightarrow x+\frac{3}{22}=\frac{3}{11}\)

\(\Rightarrow x=\frac{7}{25}+\frac{10}{3}\)                                   \(\Rightarrow x=\frac{3}{11}-\frac{3}{22}\)

       \(x=\frac{271}{75}\)                                                  \(x=\frac{3}{22}\)

c) \(\frac{8}{23}.\frac{46}{24}-x=\frac{1}{3}\)                    d) \(1-x=\frac{49}{65}.\frac{5}{7}\)

        \(\Leftrightarrow\frac{2}{3}-x=\frac{1}{3}\)                      \(\Leftrightarrow1-x=\frac{7}{13}\)

                      \(\Rightarrow x=\frac{2}{3}-\frac{1}{3}\)                       \(\Rightarrow x=1-\frac{7}{13}\)

                           \(x=\frac{1}{3}\)                                         \(x=\frac{6}{13}\)

a) Ta có: \(\frac{x}{9}=\frac{-12}{27}\)

=> \(27.x=-12.9\)

=> \(27x=-108\)

=> \(x=108:27\)

=>\(x=4\)

#)Giải :

a) x + 2x + 3x + ... + 100x = - 213

=> 100x + ( 2 + 3 + 4 + ... + 100 ) = - 213 

=> 100x + 5049 = - 213 

<=> 100x = - 5262

<=> x = - 52,62

#)Giải :

b) \(\frac{1}{2}x-\frac{1}{3}=\frac{1}{4}x-\frac{1}{6}\)

\(\Rightarrow\frac{1}{2}x+\frac{1}{4}x=\frac{1}{3}+\frac{1}{6}\)

\(\Rightarrow\frac{1}{2}x+\frac{1}{4}x=\frac{1}{2}\)

\(\Rightarrow\left(\frac{1}{2}+\frac{1}{4}\right)x=\frac{1}{2}\)

\(\Rightarrow\frac{3}{4}x=\frac{1}{2}\)

\(\Leftrightarrow x=\frac{2}{3}\)

a) x + 2x + 3x + ... +100x = -213

=>  x . (1 + 2 + 3 +... + 100) = - 213

=> x . 5050 = -213

=> x           = - 213 : 5050

=> x           = -213/5050

b) \(\frac{1}{2}x-\frac{1}{3}=\frac{1}{4}x-\frac{1}{6}\)

=> \(\frac{1}{2}x-\frac{1}{4}x=\frac{1}{3}-\frac{1}{6}\)

=> \(x.\left(\frac{1}{2}-\frac{1}{4}\right)=\frac{1}{6}\)

=> \(x.\frac{1}{4}=\frac{1}{6}\)

=> \(x=\frac{1}{6}:\frac{1}{4}\)

=> \(x=\frac{2}{3}\)

c) 3(x-2) + 2(x-1) = 10

=> 3x - 6 + 2x - 2 = 10

=> 3x + 2x - 6 - 2 = 10

=> 5x - 8 = 10

=> 5x = 10 + 8

=> 5x = 18

=> x = 18:5

=> x = 3,6

d) \(\frac{x+1}{3}=\frac{x-2}{4}\)

=> \(4\left(x+1\right)=3\left(x-2\right)\)

=>\(4x+4=3x-6\)

=> \(4x-3x=-4-6\)

=> \(x=-10\)

1, Tính tổng:

\(C=\frac{5}{7}\cdot\frac{5}{11}+\frac{5}{7}\cdot\frac{2}{11}-\frac{5}{7}\cdot\frac{14}{11}\)

\(=\frac{5}{7}\cdot\left(\frac{5}{11}+\frac{2}{11}-\frac{14}{11}\right)=\frac{5}{7}\cdot\frac{-7}{11}=\frac{-5}{11}\)

2, Tìm x:

\(x+\frac{5}{5\cdot9}+\frac{4}{9\cdot13}+\frac{4}{13\cdot17}+...+\frac{4}{41\cdot45}=\frac{-37}{45}\)

\(\Rightarrow x+\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+...+\frac{1}{41}-\frac{1}{45}=\frac{-37}{45}\)

\(\Rightarrow x+\frac{1}{5}-\frac{1}{45}=\frac{-37}{45}\Rightarrow x+\frac{9}{45}-\frac{1}{45}=\frac{-37}{45}\)

\(\Rightarrow x+\frac{8}{45}=\frac{-37}{45}\Rightarrow x=\frac{-37}{45}-\frac{8}{45}=\frac{-45}{45}=-1\)

- Các bài tìm x còn lại bạn cứ theo trình tự thực hiện phép tính mà làm nhé!

\(C=\frac{5}{7}\cdot\frac{5}{11}+\frac{5}{7}\cdot\frac{2}{11}-\frac{5}{7}\cdot\frac{14}{11}\)

\(=\frac{5}{7}\cdot\left(\frac{5}{11}+\frac{2}{11}-\frac{14}{11}\right)\)

\(=\frac{5}{7}\cdot-\frac{7}{11}\)

\(=-\frac{5}{11}\)

\(C=\frac{5}{7}.\frac{5}{11}+\frac{5}{7}.\frac{2}{11}-\frac{5}{7}.\frac{14}{11}\)

\(\Leftrightarrow C=\frac{5}{7}\left(\frac{5}{11}+\frac{2}{11}-\frac{14}{11}\right)\)

\(\Leftrightarrow C=\frac{5}{7}\times\frac{-7}{11}\)

\(\Leftrightarrow C=\frac{-35}{77}=\frac{-5}{11}\)

- Thiếu đề bài bạn ơi !!

- Nếu là giải phương trình thì nghĩ bạn nên tự làm bởi toàn là chuyển vế cơ bản ỷ lại quá sẽ khó để làm đến phần thông hiểu, nâng cao ,.... nha

- Nếu cần kết quả để xem đúng hay sai thì ấn hỏi mình hoặc các bạn khác cũng được nha !

- Vì bạn giải xong nên mình đưa kết quả bạn soát nha :

\(a,x=-\frac{1}{4}.b,x=-\frac{19}{5}.c,x=\frac{11}{5}.d,x=-\frac{134}{81}.e,x=\frac{271}{75}\)

\(g,x=\frac{3}{22}.h,x=\frac{6}{13}.i,x=\frac{1}{3}.k,\frac{5684}{837}\)

\(\frac{x+1}{49}+1+\frac{x+2}{48}+1+\frac{x+3}{47}+1+\frac{x+4}{46}+1+\frac{x+5}{45}+1=0\)

\(\Leftrightarrow\frac{x+50}{49}+\frac{x+50}{48}+...+\frac{x+50}{45}=0\)

\(\Leftrightarrow\left(x+50\right)\left(\frac{1}{49}+\frac{1}{48}+...+\frac{1}{45}\right)=0\)

Vì 1/49+1/48+...+1/45 khác 0

Nên x+50=0

do đó x=-50

a)

\(\begin{array}{l}x.\frac{{14}}{{27}} = \frac{{ - 7}}{9}\\x = \frac{{ - 7}}{9}:\frac{{14}}{{27}}\\x = \frac{{ - 7}}{9}.\frac{{27}}{{14}}\\x = \frac{{ - 3}}{2}\end{array}\)                

Vậy \(x = \frac{{ - 3}}{2}\).

b)

\(\begin{array}{l}\left( {\frac{{ - 5}}{9}} \right):x = \frac{2}{3}\\x = \left( {\frac{{ - 5}}{9}} \right):\frac{2}{3}\\x = \left( {\frac{{ - 5}}{9}} \right).\frac{3}{2}\\x = \frac{{ - 5}}{6}\end{array}\)

Vậy \(x = \frac{{ - 5}}{6}\).

c)

\(\begin{array}{l}\frac{2}{5}:x = \frac{1}{{16}}:0,125\\\frac{2}{5}:x = \frac{1}{{16}}:\frac{1}{8}\\\frac{2}{5}:x = \frac{1}{{16}}.8\\\frac{2}{5}:x = \frac{1}{2}\\x = \frac{2}{5}:\frac{1}{2}\\x = \frac{2}{5}.2\\x = \frac{4}{5}\end{array}\)      

Vậy \(x = \frac{4}{5}\)

d)

\(\begin{array}{l} - \frac{5}{{12}}x = \frac{2}{3} - \frac{1}{2}\\ - \frac{5}{{12}}x = \frac{4}{6} - \frac{3}{6}\\ - \frac{5}{{12}}x = \frac{1}{6}\\x = \frac{1}{6}:\left( { - \frac{5}{{12}}} \right)\\x = \frac{1}{6}.\frac{{ - 12}}{5}\\x = \frac{{ - 2}}{5}\end{array}\)

Vậy \(x = \frac{{ - 2}}{5}\).

Chú ý: Khi trình bày lời giải bài tìm x, sau khi tính xong, ta phải kết luận.