xy + 3x - 7y = 21
<=> xy + 3x - 7y - 21 = 0
<=> x(y + 3) - 7(y + 3) = 0
<=> (x - 7)(y + 3) = 0
<=> \(\left[\begin{matrix}x-7=0\\y+3=0\end{matrix}\right.\Leftrightarrow\left[\begin{matrix}x=7\\y=-3\end{matrix}\right.\)
xy+ 3x- 7y= 21
x(y+3)- 7y= 21
x(y+3) = 21- 7y
x(y+3)= 7(y+3)+0
x(y+3)-7(y+3)+0
(y+3)(x-7)=0
Ta có bảng sau:
| y+3 | 0 | 3 |
| y | -3 | 0 |
| x-7 | 0 | 0 |
| x | 7 | 7 |
xy + 3x - 7y =21
\(\Leftrightarrow\) xy + 3x - 7y - 21 = 0
\(\Leftrightarrow\) x ( y + 3 ) - 7 ( y + 3 ) = 0
\(\Leftrightarrow\) ( x - 7 ) ( y + 3 ) = 0
\(\Leftrightarrow\) \(\left[\begin{matrix}x-7=0\\y+3=0\end{matrix}\right.\)
\(\Rightarrow\) \(\left[\begin{matrix}x=7\\y=-3\end{matrix}\right.\)
Bài này mk mới học
xy + 3x - 7y = 21
<=> xy + 3x - 7y - 21 = 0
<=> x(y + 3) - 7(y + 3) = 0
<=> (x - 7)(y + 3) = 0
<=> [x−7=0y+3=0⇔[x=7y=−3