x + 6 = y(x - 1)
\(\Rightarrow\) x + 6 = xy - y
\(\Rightarrow\) xy - y - x = 6
\(\Rightarrow\) y(x - 1) - x + 1 = 7
\(\Rightarrow\) y(x - 1) - (x - 1) = 7
\(\Rightarrow\) (y - 1)(x - 1) = 7
Đến đây tự làm nhé bạn.
b: =>x-1+7=y(x-1)
=>y(x-1)-x+1=7
=>(x-1)(y-1)=7
\(\Leftrightarrow\left(x-1;y-1\right)\in\left\{\left(1;7\right);\left(7;1\right);\left(-1;-7\right);\left(-7;-1\right)\right\}\)
hay \(\left(x,y\right)\in\left\{\left(2;8\right);\left(8;2\right);\left(0;-6\right);\left(-6;0\right)\right\}\)
c: =>x+2-5=y(x+2)
=>(x+2)(1-y)=5
=>(x+2)(y-1)=-5
\(\Leftrightarrow\left(x+2;y-1\right)\in\left\{\left(1;-5\right);\left(-5;1\right);\left(5;-1\right);\left(-1;5\right)\right\}\)
hay \(\left(x,y\right)\in\left\{\left(-1;-4\right);\left(-7;2\right);\left(3;0\right);\left(-3;6\right)\right\}\)
