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I wasn't able to find an easier method for this problem than this one. This is not the correct solution but will help for the time's sake.
Observe that x > 4 for any real solutions to exist.
Now, on the RHS we have 1 , which of course is a rational number.
Thus, both of x − 4 x + 1 and x x − 4 must be rational.
Case 1: x − 4 x + 1 is rational.
Since the options given are integers. We know that for any x ∈ Z , x − 4 is always an integer. Also, x = 4 .
So, x + 1 must also be an integer for x − 4 x + 1 to be rational.
∴ x ∈ { 8 , 1 5 , 2 4 , 3 5 , 4 8 , ⋯ } Note that x > 4
Case 2: x x − 4 is rational.
We know that for any x ∈ Z , x is always an integer. Also, x = 0 .
So, x − 4 must also be an integer for x x − 4 to be rational.
∴ x ∈ { 5 , 8 , 1 3 , 2 0 , 2 9 , 4 0 , ⋯ } Note that x > 4 .
At this point, I must not say that both the solution sets have only 8 common in them because I wasn't able to prove this. But it is certain that whatever the next value of x may be it will not satisfy the RHS.
But, by plugging x = 8 we see that the equation holds true. Thus, x = 8