Is this an Onto Function?

Algebra Level 4

Let f : R B f: \mathbb R \rightarrow \mathcal B is given by

f ( x ) = 2 x 8 + 6 x 4 + 4 x 2 + 3 x 8 + 3 x 4 + 2 x 2 + 1 \large f(x)=\frac{2x^8+6x^4+4x^2+3}{x^8+3x^4+2x^2+1}

How many integral values does B \mathcal B includes for f ( x ) f(x) to be onto function?


Wanna try more problems on functions ?


The answer is 1.

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1 solution

U Z
Oct 14, 2014

f ( x ) = 2 ( x 8 + 3 x 4 + 2 x 2 + 1 ) x 8 + 3 x 4 + 2 x 2 + 1 f(x) = \frac{2(x^{8} + 3x^{4} + 2x^{2} +1)}{x^{8} + 3x^{4} + 2x^{2} + 1} + 1 x 8 + 3 x 4 + 2 x 2 + 1 + \frac{1}{x^{8} + 3x^{4} + 2x^{2} + 1}

thus

f ( x ) = 2 + 1 x 8 + 3 x 4 + 2 x 2 + 1 f(x) = 2 + \frac{1}{x^{8} + 3x^{4} + 2x^{2} + 1}

for f(x) to be integer 1 x 8 + 3 x 4 + 2 x 2 + 1 \frac{1}{x^{8} + 3x^{4} + 2x^{2} + 1} should be an integer

solving it over reals we find the fraction becomes integer only for x = 0

therefore only one solution

Exactly. Also Range of f ( x ) f(x) is ( 2 , 3 ] \large (2,3]

Sandeep Bhardwaj - 6 years, 8 months ago

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sir how can we make graph of this function because graphical solutions are very attractive

U Z - 6 years, 8 months ago

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At x=0, the function will have maximum value i.e. 3 and As value of x will increase , the function will start decreasing and will tend to value of 2 at x tending to \infty . You can y=2 line will be asymptote at the graph of f ( x ) f(x) . The graph will be symmetrical about y-axis, because of being e v e n even function.

Sandeep Bhardwaj - 6 years, 8 months ago

It is an even function And increasing the value of of x Decreases the function.

Rishabh Deep Singh - 5 years, 2 months ago

Exactly :)

Aniket Sanghi - 5 years, 2 months ago

exactly the same way :)

Abhinav Raichur - 6 years, 8 months ago

Yeah I think that was the only method to solve .....but who can tell there may be more..........😃

ashutosh mahapatra - 6 years ago

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