In which option are all coefficients real and variable powers valid?

Correct answer: \(2x^2-\pi x+\sqrt{11}\)

\(2x^2-\pi x+\sqrt{11}\) is a polynomial because its coefficients \(2\), \(-\pi\), and \(\sqrt{11}\) are real numbers, and the powers of \(x\) are \(2\), \(1\), and \(0\), all non-negative integers. \(\sqrt{x}=x^{\frac12}\) has a fractional exponent, while \(\frac{1}{x}=x^{-1}\) and \(x^{-\pi}\) have negative exponents, so they are not polynomials. Exam tip: variable exponents in a polynomial can only be \(0,1,2,\ldots\); coefficients may be any real numbers, including \(\pi\) and \(\sqrt{11}\).