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Exercises Equations and inequalities

Example 4 from Algebra and Trigonometry, 2.4 Complex Numbers

Multiplying a Complex Number by a Real Number

Find the product $4 (2 + 5 i) .$

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Solution
Distribute the 4.

$\begin{matrix} 4 (2 + 5 i) & = & (4 \cdot 2) + (4 \cdot 5 i) \\ = & 8 + 20 i \end{matrix}$

Your turn

The book's Try It right after this example: same idea, new numbers. Only the answer is given.

Find the product: $\frac{1}{2} (5 - 2 i) .$

How did it go?

PreviousAdding and Subtracting Complex Numbers Next Multiplying a Complex Number by a Complex Number

From Algebra and Trigonometry (1st edition) by OpenStax (Rice University), section 2.4, licensed under CC BY 4.0. Original at openstax.org. We split the solution into steps; the words, numbers and figures are the book's. OpenStax doesn't endorse this site.