TK: Câu hỏi của Hà Phương Linh - Toán lớp 9 - Học trực tuyến OLM

\(x^2-xy-2022x+2023y-2024=0\\\Leftrightarrow (x^2-2023x)-(xy-2023y)+(x-2023)-1=0\\\Leftrightarrow x(x-2023)-y(x-2023)+(x-2023)=1\\\Leftrightarrow(x-2023)(x-y+1)=1\)

Vì \(x,y\) nguyên nên \(x-2023;x-y+1\) có giá trị nguyên

mà \(\left(x-2023\right)\left(x-y+1\right)=1\)

nên ta có các trường hợp xảy ra là:

\(\left[{}\begin{matrix}\left\{{}\begin{matrix}x-2023=1\\x-y+1=1\end{matrix}\right.\\\left\{{}\begin{matrix}x-2023=-1\\x-y+1=-1\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=y=2024\left(tm\right)\\\left\{{}\begin{matrix}x=2022\\y=2024\end{matrix}\right.\left(tm\right)\end{matrix}\right.\)

Vậy \(\left(x;y\right)=\left(2024;2024\right);\left(2022;2024\right)\).

\(\text{#}Toru\)

\(x^2y + xy - 2x^2 - 3x + 4 = 0\)

=>\(y(x^2 + x) = 2x^2 + 3x - 4\) (1)

TH1: \(x^2+x=0\)

=>x(x+1)=0

=>x=0 hoặc x=-1

Khi x=0 thì (1): \(y\left(0^2+0\right)=2\cdot0^2+3\cdot0-4=-4\)

=>0y=-4(vô lý)

Khi x=-1 thì \(y\left\lbrack\left(-1\right)^2+\left(-1\right)\right\rbrack=2\cdot\left(-1\right)^2+3\cdot\left(-1\right)-4\)

=>0y=2-3-4=-1-4=-5(vô lý)

TH2: x^2+x<>0

=>\(y=\frac{2x^2+3x-4}{x^2+x}=\frac{2x^2+2x+x-4}{x^2+x}=2+\frac{x-4}{x^2+x}\)

Để y nguyên thì x-4⋮x(x+1)

=>x-4⋮x và x-4⋮x+1

=>-4⋮x và x+1-5⋮x+1

=>x∈{1;-1;2;-2;4;-4} và -5⋮x+1

=>x∈{1;-1;2;-2;4;-4} và x+1∈{1;-1;5;-5}

=>x∈{1;-1;2;-2;4;-4} và x∈{0;-2;4;-6}

=>x∈{-2;4}

Khi x=-2 thì \(y=2+\frac{-2-4}{\left(-2\right)^2+\left(-2\right)}=2+\frac{-6}{4-2}=2+\frac{-6}{2}=2-3=-1\)

=>Nhận

Khi x=4 thì \(y=2+\frac{4-4}{4^2-4}=2\) (nhận)

\(\Leftrightarrow2x^2-x+1=xy+2y\)

\(\Leftrightarrow2x^2-x+1=y\left(x+2\right)\)

\(\Leftrightarrow y=\dfrac{2x^2-x+1}{x+2}=2x-5+\dfrac{11}{x+2}\)

Do y nguyên \(\Rightarrow\dfrac{11}{x+2}\) nguyên \(\Rightarrow x+2=Ư\left(11\right)\)

Mà x nguyên dương \(\Rightarrow x+2\ge3\Rightarrow x+2=11\Rightarrow x=9\)

\(\Rightarrow y=14\)

Vậy \(\left(x;y\right)=\left(9;14\right)\)

`xy-2x+y+1=0`

`x(y-2)+(y-2)+3=0`

`(y-2)(x+1)=-3=-3.1=-1.3`

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

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

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

`@{(x+1=1),(y-2=-3):}=>{(x=0),(y=-1):}`

\(\Leftrightarrow y\left(x-2\right)+\left(x-2\right)-1=0\)

\(\Leftrightarrow\left(x-2\right)\left(y+1\right)=1\)

TH1:

\(\left\{{}\begin{matrix}x-2=1\\y+1=1\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=3\\y=0\end{matrix}\right.\)

TH2:

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

Vậy (x;y) = (3;0); ( 1;-2)