How many integer points does the domain of the given function contain?
f ( x ) = { x + 1 } − x 2 + 2 x 1
Notation: { x } denotes the fractional part function which is given by: { x } = x − ⌊ x ⌋ for x ∈ R .
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Here we go,
f ( x ) = { x + 1 } − x 2 + 2 x 1
So we know { x + 1 } − x 2 + 2 x > 0
⟹ { x + 1 } > x 2 − 2 x
Again we know that,
⟹ 0 ≤ { x + 1 } < 1
Hence it is clear that
⟹ x 2 − 2 x < 1
⟹ x 2 − 2 x + 1 < 2
⟹ ( x − 1 ) 2 < 2
⟹ ( x − 1 ) 2 − 2 2 < 0
⟹ ( x − 1 − 2 ) ( x − 1 + 2 < 0
So x ∈ ( 1 − 2 , 1 + 2 )
Now see that we have x = 0 , 1 , 2 as integers
But by observation x = 0 and x = 2 makes f ( x ) undefined.
⟹ Only integral x which satisfies is x = 1
So 1 integer points the domain of the given function contains.
Although your answer is correct, your domain isn't. You forgot some other conditions there. The domain actually is
x ∈ ( 2 3 − 1 3 , 0 ) ∪ ( 0 , 2 )
The question can be solved graphically quite easily . Make the graph of x^2-2x and {x} . Notic the intersection points of the parabola and {x} graph.then we find that the domain is from ((3-√(13))/2,2)-{0}
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For integral points, { x + 1 } = 0
So we must have, 2 x > x 2 ⟹ x ( 2 − x ) > 0 which is satisfied by x = 1