Bài 7:
a, x + 2y = xy + 2
=> x + 2y - xy = 2
x.(1 - y ) - 2.( 1 -y ) = 0
( x - 2 ).(1- y ) = o
=> \left\{\begin{matrix} x - 2 = 0 => x = 2 & & \\ 1 - y = 0 => y = 1 & & \end{matrix}\right.
b, xy = x + y
=> xy - x - y = 0
x.(y - 1 ) - (y - 1) = 1
( x - 1 ).(y - 1) = 1
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