Is there such polynomials that exist

integerspolynomialsroots

Let f be a polynomial of degree 3 with integer coefficients such that f(0) = 3 and f(1) = 11. If f has exactly 2 integer roots, how many such polynomials f such exist?

Approach:

f(0) = 3 so constant term is 3

f(x) = ax^3 + bx^2 + cx + 3

and it has exactly 2 integer roots.

since integer coefficients, then the roots are integers

So there is one root that is multiplicity 2.

Question:

Is there such polynomials that exist?

Best Answer

No polynomial $p(x)$ with integer coefficients such that $p(0)=3$ and $p(1)=11$ has integer roots. Let $n\in\Bbb Z$. If $n$ is even, then $n\equiv0\pmod2$ and therefore $p(n)\equiv p(0)(=3)\pmod 2$. So, $p(n)$ is odd. And if $n$ is even, then $n\equiv1\pmod2$ and therefore $p(n)\equiv p(1)(=11)\pmod2$. So, again, $p(n)$ is odd. Since $p(n)$ is always odd, it cannot be equal to $0$.

Related Question