Subtracting complex numbers | Imaginary and complex numbers | Precalculus | Khan Academy | Summary and Q&A

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February 13, 2014
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Khan Academy
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Subtracting complex numbers | Imaginary and complex numbers | Precalculus | Khan Academy

TL;DR

Learn how to subtract complex numbers and visually represent the result on an Argand diagram.

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Questions & Answers

Q: How can complex numbers be subtracted?

Complex numbers can be subtracted by subtracting their real parts and imaginary parts separately. For example, to subtract (6 + 2i) from (2 - i), we subtract the real parts (2 - 6 = -4) and the imaginary parts (-1 - 2i = -3i), resulting in the complex number -4 - 3i.

Q: How can complex number subtraction be visualized on an Argand diagram?

To visualize complex number subtraction on an Argand diagram, first plot the original complex numbers A and B as vectors. Then, add the negative of the second complex number (-B) to the first complex number (A). This is equivalent to subtracting B from A. The new head of the resulting vector C represents the complex number obtained from the subtraction.

Q: What does the negative of a complex number look like on an Argand diagram?

The negative of a complex number can be visualized by flipping the complex number vector over the origin. For example, if the complex number B is (2 - i), its negative (-B) would be (-2 + i), and when plotted on the Argand diagram, it would be reflected across the origin.

Q: How can the complex number subtraction be represented on an Argand diagram?

The complex number obtained from subtraction, C, can be represented as a vector on the Argand diagram. The tail of C is positioned at the origin, the tail of -B is placed at the head of A, and the resulting vector C extends from the tail of -B to a new head, which represents the complex number C.

Summary & Key Takeaways

  • The video teaches how to subtract complex numbers by determining the difference between their real parts and imaginary parts.

  • It explains how to visualize complex number subtraction on an Argand diagram by adding the negative of the second complex number to the first complex number.

  • The resulting complex number can be represented as a vector on the diagram.

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