Question

Giải hệ phương trình bằng phương pháp thế:

3x + |y| = -1

2x + y = -4

Answer 1

2x+y=-4

\(\Leftrightarrow2x=-4-y\)

\(\Leftrightarrow x=\dfrac{-y-4}{2}\)

Ta có: 3x+|y|=-1

\(\Leftrightarrow\dfrac{-3y-12}{2}+\left|y\right|=-1\)

\(\Leftrightarrow\left|y\right|=\dfrac{-2+3y+12}{2}=\dfrac{3y+10}{2}\)

\(\Leftrightarrow\left[{}\begin{matrix}y=\dfrac{3}{2}y+5\left(y\ge0\right)\\y=-\dfrac{3}{2}y+5\left(y< 0\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\dfrac{-1}{2}y=5\\\dfrac{5}{2}y=5\end{matrix}\right.\Leftrightarrow y\in\varnothing\)

Answer 2

x=-1 ,y=-2

Answer 3

x = 3; y = -10