Which of the following describes a second-degree equation?

A second-degree equation, also known as a quadratic equation, is mathematically characterized primarily by the presence of a squared term, which indicates that the highest power of the variable is 2. The standard form of a quadratic equation is given as (ax^2 + bx + c = 0), where (a), (b), and (c) are constants and (a \neq 0).

In this context, the chosen answer explicitly reflects that definition, as it contains the quadratic term (ax^2). The presence of linear terms ((bx)) and the constant term ((c)) are also part of the general structure of a quadratic, but the crucial aspect is that the (x^2) term confirms its classification as a second-degree polynomial.

The other choices represent different types of equations. For instance, the first option describes a first-degree equation or a linear equation due to the absence of a squared term. The third choice also describes a linear equation with two variables while the last choice displays a third-degree equation because of the cubic term (ax^3). Hence, the uniqueness of the second-degree polynomial (ax^2 + bx + c = 0) is