Ta có:\(\left(\dfrac{-5}{4}x+2,15\right)\left[2\dfrac{3}{7}-\left(\dfrac{-1}{2}x\right)\right]=0\)
\(\Rightarrow\left[{}\begin{matrix}\dfrac{-5}{4}x+2,15=0\\2\dfrac{3}{7}-\left(\dfrac{-1}{2}x\right)=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}\dfrac{-5}{4}x=\dfrac{-43}{20}\\\dfrac{-1}{2}x=\dfrac{17}{7}\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=\dfrac{43}{25}\\x=\dfrac{-34}{7}\end{matrix}\right.\)
Vậy \(\left[{}\begin{matrix}x=\dfrac{43}{25}\\x=\dfrac{-34}{7}\end{matrix}\right.\)
e) Ta có: \(\left(-\dfrac{5}{4}x+2.15\right)\left[2\dfrac{3}{7}-\left(-\dfrac{1}{2}x\right)\right]=0\)
\(\Leftrightarrow\left(-\dfrac{5}{4}x+\dfrac{43}{20}\right)\left(\dfrac{17}{7}+\dfrac{1}{2}x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{-5}{4}x=\dfrac{-43}{20}\\\dfrac{1}{2}x=-\dfrac{17}{7}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{43}{25}\\x=\dfrac{-34}{7}\end{matrix}\right.\)
biết:
b./ 
c*./ 
b/ 
c/ 
= 
e/ 
= 
và x + y = 22 f/ 
và 
e) 9x =81 
h) 
và x + y= -21 i) 
và 3x - 2y = -2
và 3x – 2y – z = -29