Argand diagrams – basics
What is an Argand diagram?
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An Argand diagram is a geometrical way to represent complex numbers as either a point or a vector in two-dimensional space
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We can represent the complex number
by the point with cartesian coordinate
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The real component is represented by points on the x-axis, called the real axis, Re
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The imaginary component is represented by points on the y-axis, called the imaginary axis, Im


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You may be asked to show roots of an equation in an Argand diagram
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First solve the equation
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Draw a quick sketch, only adding essential information to the axes
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Plot the points and label clearly
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How can I use an Argand diagram to visualise |z1 + z2| and |z1 – z2|?
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Plot two complex numbers z1 and z2
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Draw a line from the origin to each complex number
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Form a parallelogram using the two lines as two adjacent sides
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The modulus of their sum |z1 + z2| will be the length of the diagonal of the parallelogram starting at the origin
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The modulus of their difference |z1 – z2| will be the length of the diagonal between the two complex numbers

Worked Example
a) Plot the complex numbers z1 = 2 + 2i and z2 = 3 – 4i as points on an Argand diagram.

b) Write down the complex numbers represented by the points A and B on the Argand diagram below.
Responses