Chapter 4 Quadratic Functions and Factoring - 4.6 Perform Operations with Complex Numbers - 4.6 Exercises - Skill Practice - Page 280: 57

The solution is not written in standard form, $a+bi$. The correct answer is $6+7i$

The solution is not written in standard form, $a+bi$. Using $i^{2}=-1$, we correct the error. $(1+2i)(4-i)$ $=4-i+8i-2i^{2}$ $=-2i^{2}+7i+4$ $=-2(-1)+7i+4\qquad$ ...simplify $=2+7i+4\qquad$ ...simplify $=6+7i$