# Mathematics for Technology II (Math 2131) Durham College, Mathematics
Free • 0 lessons
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• 14 week duration
• ##### Solving Systems of Equations

This unit introduces how to systematically solve a system of equations, namely linear equations. Examples of non-linear systems, including systems of 3 unknowns will be of emphasis.

• ##### Graphs of Trigonometric Functions

The unit focuses primarily on how to graph periodic sinusoidal functions, and how to identify features of a waveform to produce an equation by inspection.

• ##### Polar Coordinate Functions

An introduction to the polar coordinate system.

• ##### Complex Numbers

This unit is an extension of what was introduced in Math 1131. To learn how to work with radicals, knowing your exponent laws in crucial. Hence, this unit begins with a thorough review.

• ##### Logarithmic Functions

This chapter introduces you to exponential functions, and how they can be solved using logarithms.

• ##### Trigonometric Identities and Equations
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• ##### Analytic Geometry
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# Multiplying Complex Numbers

Imaginary and complex numbers are multiplied the same way you multiply polynomials, with the addition of what you learned in the previous lesson about i when raised to varying exponents. Examples are shown below:

Similarly, this idea can be expanded to imaginary numbers found within larger algebraic expressions found in polynomials. For example:

Starting with (1), you’d expand the factor 3 into the binomial (5 + 2i), giving you: 15 + 6i. In question (2), 3i×2 equals 6i and 3i×(–4i) equals –12i². Together, 6i – 12i² = 6i + 12 ⇒ 12 + 6i. For question (3), you’d have to use the foil method (linked), giving you: –12 + 15i + 8i – 20i² ⇒ –12 + 23i + 20 ⇒ 8 + 23i.

As discussed briefly in the previous lesson, the conjugate of a complex number is one that changes the sign of the imaginary portion. In case you’re asked to multiply a complex number by its conjugate, follow the steps outlined in the video below:

# Beware of this common mistake

If you’re asked to multiply, for example:

$\sqrt{–4}×\sqrt{–4}\phantom{\rule{0ex}{0ex}}$

$\sqrt{–4}×\sqrt{–4}\ne \sqrt{–4×–4}=\sqrt{16}=4\phantom{\rule{0ex}{0ex}}$
$\sqrt{4}\sqrt{–1}×\sqrt{4}\sqrt{–1}\phantom{\rule{0ex}{0ex}}\sqrt{4}\sqrt{4}\sqrt{–1}\sqrt{–1}\to {4}^{1}{2}}{4}^{1}{2}}\sqrt{–1}\sqrt{–1}\phantom{\rule{0ex}{0ex}}4{i}^{2}\phantom{\rule{0ex}{0ex}}4\left(–1\right)\phantom{\rule{0ex}{0ex}}=–4$