For a term like xnx^nxn to be part of a polynomial , the exponent nnn must be a non‑negative integer (that is, n=0,1,2,3,…n=0,1,2,3,\dots n=0,1,2,3,…).

Quick Scoop: What kind of number is nnn?

When you see something like:

f(x)=anxn+an−1xn−1+⋯+a1x+a0,f(x)=a_nx^n+a_{n-1}x^{n-1}+\dots +a_1x+a_0,f(x)=an​xn+an−1​xn−1+⋯+a1​x+a0​,

this is the general form of a polynomial.

In this definition:

  • Each exponent (like n,n−1,…,2,1,0n,n-1,\dots,2,1,0n,n−1,…,2,1,0) is a non‑negative integer.
  • The coefficients a0,a1,…,ana_0,a_1,\dots,a_na0​,a1​,…,an​ are real numbers (or sometimes complex numbers, depending on the context).

So in the term xnx^nxn:

  • nnn cannot be negative (so no x−1,x−2,…x^{-1},x^{-2},\dots x−1,x−2,…).
  • nnn cannot be a fraction or decimal (so no x1/2,x0.3,…x^{1/2},x^{0.3},\dots x1/2,x0.3,…).
  • nnn cannot be irrational (so no x2x^{\sqrt{2}}x2​).

It must be a whole number starting from 0.

Why non‑negative integers?

Polynomials are defined as finite sums of terms of the form axkax^kaxk, where:

  • aaa is a real number (the coefficient).
  • kkk is a non‑negative integer.

If you allow:

  • Negative exponents → you get rational functions , not polynomials (for example, x−1=1/xx^{-1}=1/xx−1=1/x).
  • Fractional exponents → you get radical functions or more general power functions, not polynomials (for example, x1/2=xx^{1/2}=\sqrt{x}x1/2=x​).

That’s why textbooks and courses always emphasize: “Exponents in a polynomial must be non‑negative integers.”

Mini example

  • 2x3−5x+72x^3-5x+72x3−5x+7 is a polynomial: exponents are 3,1,03,1,03,1,0 → all non‑negative integers.
  • 4x−2+x4x^{-2}+x4x−2+x is not a polynomial: exponent −2-2−2 is negative.
  • 3x1/2+13x^{1/2}+13x1/2+1 is not a polynomial: exponent 1/21/21/2 is fractional.

So, answering your exact question:

If xnx^nxn is a term of a polynomial, what type of number is nnn?

nnn is a non‑negative integer (0, 1, 2, 3, …).

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