This is a Test of Mathematics Solution Subjective 175 (from ISI Entrance). The book, Test of Mathematics at 10+2 Level is Published by East West Press. This problem book is indispensable for the preparation of I.S.I. B.Stat and B.Math Entrance.
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Let \(\text{P(x)}=x^n+a_{n-1}x^{n-1}+a_{n-2}x^{n-2}+\dots+a_{1}x+a_{0}\) be a polynomial with integer coefficients,such that,\(\text{P(0) and P(1)}\) are odd integers.Show that
(a)\(\text{P(x)}\) does not have any even integer roots.
(b)\(\text{P(x)}\) does not have any odd integer roots.
Given the two statements (a) and (b) above it is clear that if we can prove that \(\text{P(x)}\) has no integer roots,then we are done.
Let us assume \(\text{P(x)}\) has an integer root \(\text{ a}\).
Then we can write,
$$ \text{P(x)=(x-a)Q(x)}\dots(1)$$
where,\(\text{Q}\)is any function of \(\text{ x}\).
Now ,putting \(\text{x=0,1}\) in \(\text{ 1}\),we get
$$\text{P(0)=(-a)Q(0)}\dots(2)$$
and,
$$\text{P(1)=(1-a)Q(1)}\dots(3)$$
now as \(\text{(1-a)}\) and \(\ \text{(-a)}\),are consecutive integers \( \text{(2)}\) and \(\text{(3)}\)
cannot be both odd,
which means that \(\text{P(0),P(1)}\) cannot be both odd,given whatever \(\text{Q(0) and Q(1)}\) are.
So,it is a contradiction!!.
So,we can conclude that there exists no integer solution of \(\text{P(x)}\).
Hence,we are done.
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