FP1 Topic 3: Complex numbers
Modulus and argument of complex numbers
Since complex numbers have two parts - their real and imaginary parts - they can be plotted on a graph. The real part is plotted along the horizontal x-axis and the imaginary part is plotted on the vertical y-axis. Such a diagram is known as an Argand diagram. This Argand diagram shows the modulus, |a| or |OA|, and the argument, arg(a), shown in degrees, of the complex number a. If the coordinates of the point A are (b,c) then a = b+ic |a| = \sqrt{b^2+c^2} and arg(a) = \tan^{-1}\displaystyle \frac{c}{b}

Please enable Java for an interactive construction (with Cinderella).

Summary the modulus |OA| is the length of the line segment OA. the argument arg(a) is measured anticlockwise from the positive real axis Uses Cinderella interactive geometry.