The total number of integers pairs (x, y) satisfying the equation x + y = xy is
xy = x + y
=> xy - x - y = 0
=> xy - x - y + 1 = 1
=> (x - 1) (y - 1) = 1
=> Both x - 1 and y - 1 have to be equal to 1 or -1.
So, values taken by (x,y) are (2,2) and (0,0).
=> 2 solutions
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