This lesson continues the idea from the previous lesson that when complex numbers are combined, the result is also a complex number and can be written in the form \(a+bi\), where \(a\) and \(b\) are real numbers. In this lesson, students use the fact that \(i^2=\text1\) to multiply imaginary numbers, and use the strategies they develop to multiply complex numbers by writing the \(i^2\) terms as real numbers.
Students also make use of the familiar structure of distributing terms to find the result of multiplying two complex numbers (MP7). To organize their thinking, they can use the same kind of diagrams they used in a previous unit to multiply polynomials.
Lesson overview
 13.1 Warmup: \(i\) Squared (5 minutes)
 13.2 Activity: Multiplying Imaginary Numbers (15 minutes)

13.3 Activity: Multiplying Complex Numbers (15 minutes)
 Includes "Are you Ready for More?" extension problem
 Lesson Synthesis
 13.4 Cooldown: Squares and Imaginary Numbers (5 minutes)
Learning goals:
 Calculate the result of multiplying two complex numbers.
 Justify that two equivalent expressions involving complex numbers are equivalent, using the fact that \(i^2=\text1\).
Learning goals (student facing):
 Let's multiply complex numbers.
Learning targets (student facing):
 I can multiply complex numbers.
Standards:
 This lesson builds on the standard: CCSS.HSNRN.A.2MS.NRN.2MO.A1.NQ.A.2
 This lesson builds towards the standards: CCSS.HSNCN.A.1MS.NCN.1CCSS.HSNCN.A.2MS.NCN.2MO.A2.NQ.B.5MO.A2.NQ.B.6
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