Find the number of real satisfying the equation .
Notations :
denotes the fractional part function .
denotes the floor function .
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Let ⌊ x ⌋ = n and { x } = r . Then, applying Simon's favorite factoring trick,
n r − 2 n = r − 1
n ( r − 2 ) − r + 1 + ( 1 ) = 0 + ( 1 )
n ( r − 2 ) − ( r − 2 ) = 1
( n − 1 ) ( r − 2 ) = 1
Now, considering the range of r , we know that 0 ≤ r < 1 .
So, − 2 ≤ r − 2 < − 1 .
Multiplying the inequality by n − 1 , with n = 1 , we get
− 2 ( n − 1 ) ≤ ( r − 2 ) ( n − 1 ) < − ( n − 1 )
Dealing with both sides of the inequality separately, we have the following for the first part of the inequality:
− 2 ( n − 1 ) ≤ ( r − 2 ) ( n − 1 )
− 2 ( n − 1 ) ≤ 1
2 ( n − 1 ) ≥ − 1
( n − 1 ) ≥ − 1 / 2 or n ≥ 1 / 2
Now for the second part of the inequality:
1 < − ( n − 1 )
− 1 > ( n − 1 ) or n < 0 , which is a contradiction to the previous result obtained.
As n cannot be greater than 1 / 2 and less than 0 at the same time, we conclude there are no solutions for n and so there are no solutions for x .