\(\Leftrightarrow\left[{}\begin{matrix}2x-3=0\\\dfrac{1}{4}x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=1:\dfrac{1}{4}=4\end{matrix}\right.\)

\(2x=-\dfrac{5}{3}-\dfrac{1}{2}=\dfrac{-13}{6}\Rightarrow x=-\dfrac{13}{6}:2=-\dfrac{13}{12}\)

2x\(\dfrac{1}{2}\)=\(-\dfrac{5}{3}\)

\(\Rightarrow2\)x=\(-\dfrac{13}{6}\)

\(\Rightarrow\)x=\(-\dfrac{13}{12}\)

bạn đăng tách ra nhé 

a, Theo tc dãy tỉ số bằng nhau ta có

\(\dfrac{x}{2}=\dfrac{y}{3}=\dfrac{z}{4}=\dfrac{x+y+z}{2+3+4}=\dfrac{9}{9}=1\Rightarrow x=2;y=3;z=4\)

hình như hình sai rồi bạn 

\(\dfrac{5}{3}=5:3\)

Vậy \(2\) số đó là \(5\) và \(3\)

\(\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{19.20}\)

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{19}-\dfrac{1}{20}\)

\(=\dfrac{1}{2}-\dfrac{1}{20}\)

\(=\dfrac{9}{20}\)

\(A=\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{19.20}\)

\(A=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{19}-\dfrac{1}{20}\)

\(A=\dfrac{1}{2}-\dfrac{1}{20}=\dfrac{10}{20}-\dfrac{1}{20}=\dfrac{9}{20}\)