Bạn tham khảo nha:
a) xy-3x+7y=21
⇔xy-3x+7y-21=0
⇔(xy-3x)+(7y-21)=0
⇔x(y-3)+7(y-3)=0
⇔(y-3)(x+7)=0
⇔\(\left[ \begin{array}{l}y-3=0\\x+7=0\end{array} \right.\)⇔\(\left[ \begin{array}{l}y=3\\x=-7\end{array} \right.\)
Vậy x=-7; y=3
b) xy+3x-7y=21
⇔xy+3x-7y-21=0
⇔(xy+3x)-(7y+21)=0
⇔x(y+3)-7(y-3)=0
⇔(y+3)(x-7)=0
⇔\(\left[ \begin{array}{l}y+3=0\\x-7=0\end{array} \right.\)⇔\(\left[ \begin{array}{l}y=-3\\x=7\end{array} \right.\)
Vậy x=7; y=-3
c) xy+5y-2x=10
⇔xy+5y-2x=10
⇔xy+5y-2x-10=0
⇔(xy+5y)-(2x+10)=0
⇔y(x+5)-2(x+5)=0
⇔(x+5)(y-2)=0
⇔\(\left[ \begin{array}{l}x+5=0\\y-2=0\end{array} \right.\)⇔\(\left[ \begin{array}{l}x=-5\\y=2\end{array} \right.\)
Vậy x=-5; y=2.
