Which statement best describes the equation x5 + x3 – 14 = 0?

An equation is quadratic in form when its powers can be written as 2n, n, and 0, so a substitution such as u = x^n turns it into a quadratic. Here the powers are 5, 3, and 0; there is no n for which 5 = 2n and 3 = n. Thus it cannot be rewritten as a second-degree polynomial. The fact that the exponents 5 and 3 differ by 2 is not enough to make the equation quadratic in form.

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