हिंदी

Argand Diagram or Complex Plane

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Topics

Estimated time: 7 minutes
  • Modulus of z
  • Argument of z
  • Argument of z in different quadrants/axes - Properties of modulus of complex numbers, Properties of arguments 
  • Polar & Exponential form of C.N.
Maharashtra State Board: Class 12

Key Points: Argand Diagram or Complex Plane

1. Representation

  • z = a + ib → point (a, b)
  • X-axis → Real part (Re)
  • Y-axis → Imaginary part (Im)

2. Modulus

  • |z| = distance from origin
  • |z| = √(a² + b²)

3. Argument (θ)

  • Angle made with +X-axis (anticlockwise)
  • θ = tan⁻¹(b/a)
z = a + ib Quadrant / Axis θ = arg z
a > 0, b = 0 On the positive real (X) axis θ = 0
a > 0, b > 0 Quadrant I \[\Theta=\tan^{-1}\left(\frac{\mathrm{b}}{\mathrm{a}}\right)\]
a = 0, b > 0 On the positive imaginary (Y) axis θ = π/2
a < 0, b > 0 Quadrant II \[\theta=\pi-\tan^{-1}\left|\frac{\mathrm{b}}{\mathrm{a}}\right|\]
a < 0, b = 0 On the negative real (X) axis θ = π
a < 0, b < 0 Quadrant III \[\Theta=\pi+\tan^{-1}\left|\frac{\mathrm{b}}{\mathrm{a}}\right|\]
\[\theta=\tan^{-1}\left|\frac{\mathrm{b}}{\mathrm{a}}\right|-\pi\]
a = 0, b < 0 On the negative imaginary (Y) axis θ = 3π/2
a > 0, b < 0 Quadrant IV \[\Theta=2\pi-\tan^{-1}\left|\frac{\mathrm{b}}{\mathrm{a}}\right|\]
Maharashtra State Board: Class 1

Definition: Polar Form of a Complex Number

The polar form of a complex number z = x + iy is

z = r(cos θ + i sin θ), where x = r cos θ, y = r sin θ and r = \[r=\sqrt{x^{2}+y^{2}}\].

Maharashtra State Board: Class 12

Definition: Exponential Form or Euler’s Form

∴ z = a + ib = r(cos θ + i sin θ) = re,

where r = |z| and θ = arg z is called an exponential form of a complex number.

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