Saturday, September 13, 2014

What is the maximum integer value of the fraction ( 2x^2+4x+5 )/( x^2+2x+2 ) if x is real number ?

We'll note the fraction as
E(x).


E(x) =
(2x^2+4x+5)/(x^2+2x+2)


We'll re-write the numerator in this
way:


2x^2+4x+5 = x^2 + 2x + 2 + x^2 + 2x + 2 +
1


Now, we'll group the terms from the right side such as to
create trinomials:


2x^2+4x+5 = (x^2+2x + 2) + (x^2+2x+2) +
1


We'll divide both sides by
(x^2+2x+2):


(2x^2+4x+5)/(x^2+2x+2) = (x^2+2x +
2)/(x^2+2x+2) + (x^2+2x+2)/(x^2+2x+2) + 1/(x^2+2x+2)


We'll
simplify and we'll get:


(2x^2+4x+5)/(x^2+2x+2) = 1 + 1 +
1/(x^2+2x+2)


The result of the addition of the terms from
the right side is an integer number, if and only if the fraction 1/(x^2+2x+2) is an
integer number, also.


For 1/(x^2+2x+2) to be integer,
(x^2+2x+2) = 1


Shifting 1 to the left, we'll
get:


x^2 + 2x + 1 = 0


We
notice that we've get a perfect square:


(x+1)^2 =
0


x = -1


The expression will
become:


E(x) = 1 + 1 - 1


E(x)
= 1


The maximum integer value of the given
fraction, if x is a real number, is E(x) = 1.

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