# Question #54917

b, ${x}^{2} + 2$
A quadratic is an expression or equation where the highest power of $x$ is two (2), for example ${x}^{2} + 2 x + 1$.
Answers (a) and (d) have a highest power of one (i.e. ${x}^{1} = x$), and (c) has a highest power of three (${x}^{3}$). (b) has a highest power of two (${x}^{2}$), and so is a quadratic.