Think twice

Algebra Level 3

Number of integers in the range of the function:

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

if x x can have all real values except 0 is:

3 1 0 2

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1 solution

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

So,

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

Maximum value of the expression above is obtained when 1 x 2 + x + 1 \frac{1}{x^{2} + x + 1} is maximum and vice- versa

Hence the range of f is ( 1 , 7 / 3 ] (1, 7/3]

Only Integer in this range is : 2

However , 2 cannot be achieved as it will be achieved only at x = 0 which is not in the domain of f.

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