Chapter 5 - Section 5.6 - Complex Zeros; Fundamental Theorem of Algebra - 5.6 Assess Your Understanding - Page 394: 10

The remaining zero is: $\color{blue}{\bf2-i}$

RECALL: If $a+bi$ is a zero of a polynomial function with a real number of coefficients, then its conjugate, $a-bi$, is also a zero of the function. Thus, the missing zero of the given function is the conjugate of $2+i$, which is $\color{blue}{\bf2-i}.$