Đáp án đúng nhưng cách làm này là sai

bày em cách làm với được không ạ? em tự suy ra chứ thầy cô chưa bày j cả nên là em cx chưa hiểu cho lắm mong anh giúp đỡ ạ

a) Ta thấy:
\(\frac{x}{2}=\frac{y}{3}\)\(\Rightarrow\frac{x}{2}\cdot\frac{3}{5}=\frac{y}{3}\cdot\frac{3}{5}\)\(\Rightarrow\frac{3x}{10}=\frac{y}{5}\)
Mà \(\frac{y}{5}=\frac{z}{6}\) nên ta có biểu thức: \(\frac{3x}{10}=\frac{y}{5}=\frac{z}{6}\)    ( 1 )
Biểu thức ( 1 ) tương đương với:
\(\frac{3x}{10}=\frac{3y}{15}=\frac{3z}{18}=\frac{3x+3y+3z}{10+15+18}=\frac{3\left(x+y+z\right)}{43}=\frac{3\cdot43}{43}=3\)
Khi đó:
\(\frac{3x}{10}=3\)                         \(\Rightarrow x=\frac{3\cdot10}{3}=10\)
\(\frac{3y}{15}=3\)\(\Rightarrow\frac{y}{5}=3\) \(\Rightarrow y=3\cdot5=15\)
\(\frac{3z}{18}=3\)\(\Rightarrow\frac{z}{6}=3\) \(\Rightarrow z=3\cdot6=18\)

a,  Nhân cả hai vế cho 5, ta được: X/10 = Y/15 

Tương tự ta có:                          Y/15 = Z/18  

Do đó: X/10 = Z/18 (=Y/15)

Theo đề bài, ta có: (X+Y+Z)/(10+15+18) = 43/43 = 1

                            X/10=1 => X=10

                            Y/15=1 => Y=15

                            Z/18=1 => Z=18

a ) \(1\frac{1}{2}+x=\frac{3}{7}-7\)

\(\frac{3}{2}+x=-\frac{46}{7}\)

\(x=-\frac{46}{7}-\frac{3}{2}\)

\(x=-\frac{113}{14}\)

A = \(\frac{5}{4}.\left(5-\frac{4}{3}\right).\frac{1}{11}\)

A = \(\frac{5}{44}\left(5-\frac{4}{3}\right)\)

A = \(\frac{25}{44}-\frac{5}{33}\)

A = \(\frac{25.3}{4.11.3}-\frac{5.4}{3.11.4}\)

A = \(\frac{75}{132}-\frac{20}{132}\)

A = \(\frac{55}{132}\)

B = \(\frac{3}{4}:\left(-12\right).\left(-\frac{2}{3}\right)\)

B = \(\frac{-1}{16}.\left(-\frac{2}{3}\right)\)

B = \(\frac{1}{24}\)

C = \(\frac{5}{4}:\left(-15\right).\left(-\frac{2}{5}\right)\)

C = \(\frac{-1}{12}.\left(-\frac{2}{5}\right)\)

C = \(\frac{1}{30}\)

D = \(\left(-3\right).\left(\frac{2}{3}-\frac{5}{4}\right):\left(-7\right)\)

D = \(\frac{3}{7}.\left(\frac{8}{12}-\frac{15}{12}\right)\)

D = \(\frac{3}{7}.\left(-\frac{7}{12}\right)\)

D = \(\frac{-3}{12}\)

D = \(\frac{-1}{4}\)

\(=\frac{16}{5}.\frac{15}{16}-\left(\frac{3}{4}+\frac{2}{7}\right):\left(\frac{-29}{28}\right)\)

\(=3-\left(\frac{21}{28}+\frac{8}{28}\right):\left(\frac{-29}{28}\right)\)

\(=3-\left(\frac{29}{28}\right).\left(\frac{-28}{29}\right)\)

\(=3-\left(-1\right)\)

\(=4\)

b)   \(=\left(\frac{1}{4}+\frac{25}{2}-\frac{5}{16}\right):\left(12-\frac{7}{12}:\left(\frac{3}{8}-\frac{1}{12}\right)\right)\)

       \(=\left(\frac{4}{16}+\frac{200}{16}-\frac{5}{16}\right):\left(12-\frac{7}{12}:\left(\frac{3.3}{2.3.4}-\frac{2}{2.3.4}\right)\right)\)

     \(=\left(\frac{199}{16}\right):\left(12-\frac{7}{12}:\left(\frac{9}{24}-\frac{2}{24}\right)\right)\)

      \(=\frac{199}{16}:\left(12-\frac{7}{12}.\frac{24}{7}\right)\)

    \(=\frac{199}{16}:\left(12-2\right)\)

\(=\frac{199}{16}:10\)

\(=\frac{199}{160}\)

c)   \(\left(\frac{-3}{5}+\frac{5}{11}\right):\frac{-3}{7}+\left(\frac{-2}{5}+\frac{6}{5}\right):\frac{-3}{7}\)

\(\left(\frac{-33}{55}+\frac{25}{55}\right):\frac{-3}{7}+\left(\frac{4}{5}\right):\frac{-3}{7}\)

\(\left(\frac{-8}{55}\right).\frac{-7}{3}+\frac{4}{5}.\frac{-7}{3}\)

\(\frac{-7}{3}\left(\frac{-8}{55}+\frac{4}{5}\right)\)

\(\frac{-7}{3}.\frac{36}{55}=\frac{-84}{55}\)

giờ mk phải đi ngủ r mai mk làm cho 

\(\frac{5}{4}\cdot\left(-\frac{12}{7}\right)=\frac{-60}{28}=\frac{-15}{7}\)

\(\frac{-4}{3}:\frac{13}{9}=-\frac{4}{3}\cdot\frac{9}{13}=-\frac{36}{39}=-\frac{12}{13}\)

\(-\frac{5}{7}\cdot\frac{49}{3}:\frac{7}{-6}=-\frac{5}{7}\cdot\frac{49}{3}\cdot-\frac{6}{7}=\frac{1470}{147}=10\)

\(-\frac{9}{25}:6=-\frac{9}{150}=-\frac{3}{50}\)

2.

\(\frac{7}{4}:\left(\frac{2}{3}-\frac{5}{4}\right)\cdot\left(-\frac{1}{4}\right)\)

\(=\frac{7}{4}:\left(-\frac{7}{12}\right)\cdot\left(-\frac{1}{4}\right)\)

\(=\frac{3}{4}\)

b,giá trị của x thỏa mãn đẳng thức \(-\frac{2}{3}x=\frac{4}{5}\)là 

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

\(\Rightarrow x=\frac{4}{5}:\left(-\frac{2}{3}\right)\)

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