Question

2 cách giải HPT cơ bản 
4x-y=5
2x+3y = -1

Answer 1

`{(4x-y=5),(2x+3y =-1):}`

`<=> {(4x-y=5),(4x+6y = -2):}`

`<=> -7y = 7`

`=> y = -1`

`=> x = 1`.

Answer 2

C1 

\(\left\{{}\begin{matrix}4x-y=5\\2x+3y=-1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}4x-y=5\\4x+6y=-2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-7y=7\\4x-y=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-1\\x=1\end{matrix}\right.\)

C2

\(\left\{{}\begin{matrix}4x-y=5\\2x+3y=-1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}y=4x-5\\2x+3.\left(4x-5\right)=-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=4x-5\\14x-15=-1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}y=4.1-5=-1\\x=1\end{matrix}\right.\)

Answer 3

`*** C_1:` Giải = pp thế:

`{(4x-y=5),(2x+3y=-1):}`

`<=>{(y=4x-5),(2x+3(4x-5)=-1):}`

`<=>{(y=4x-5),(2x+12x-15=-1):}`

`<=>{(y=4x-5),(14x=14):}`

`<=>{(x=1),(y=4.1-5=-1):}`

____________________________________________________

`*** C_2:` Giải = pp cộng trừ đại số.

`{(4x-y=5),(2x+3y=-1):}`

`<=>{(12x-3y=15),(2x+3y=-1):}`

`<=>{(14x=14),(2x+3y=-1):}`

`<=>{(x=1),(2.1+3y=-1):}`

`<=>{(x=1),(y=-1):}`

Answer 4

)\(C1\left\{{}\begin{matrix}4x-y=5\\2x+3y=-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=4x-5\\2x+12x-15=-1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}y=4x-5\\14x=-1+15=14\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=4.1-5=-1\\x=1\end{matrix}\right.\)

`\(C2\left\{{}\begin{matrix}4x-y=5\\2x+3y=-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4x-y=5\\4x+6y=-2\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}4x-y-4x-6y=5+2\\4x+6y=-2\end{matrix}\right.\)

`<=> -7y = 7 `

`<=> y =-1`

`=> x= (-2 - 6 .(-1))/ 4 = 1`