key term - Complex Number

Definition

A complex number is a number that can be expressed in the form of 'a + bi', where 'a' is the real part, 'b' is the imaginary part, and 'i' is the imaginary unit defined by the property that $i^2 = -1$. Complex numbers allow for the solution of equations that have no real solutions and are essential in various fields such as engineering, physics, and applied mathematics. They can be represented graphically on the complex plane, where the x-axis represents the real part and the y-axis represents the imaginary part.

5 Must Know Facts For Your Next Test

1. Complex numbers can be added, subtracted, multiplied, and divided using specific rules for their real and imaginary parts.
2. The modulus of a complex number 'a + bi' is calculated as $\sqrt{a^2 + b^2}$ and represents its distance from the origin on the complex plane.
3. Complex conjugates play an important role in operations involving complex numbers; for a complex number 'a + bi', its conjugate is 'a - bi'.
4. In trigonometric form, a complex number can be expressed as $r(\cos \theta + i \sin \theta)$, where 'r' is the modulus and '$\theta$' is the argument.
5. Euler's formula connects complex numbers with trigonometric functions: $e^{i\theta} = \cos \theta + i \sin \theta$, allowing for conversion between rectangular and polar forms.

Review Questions

• How do you perform operations such as addition and multiplication with complex numbers, and what rules apply?
  • To add complex numbers, you simply combine their real parts and their imaginary parts separately. For example, adding $(3 + 4i)$ and $(2 + 5i)$ results in $(3 + 2) + (4 + 5)i = 5 + 9i$. When multiplying complex numbers, you apply the distributive property while remembering that $i^2 = -1$. For example, $(3 + 2i)(1 + 4i)$ results in $3*1 + 3*4i + 2i*1 + 2i*4i = 3 + 12i + 2i - 8 = -5 + 14i$.
• Describe how to convert a complex number from rectangular form to polar form and explain why this transformation is useful.
  • To convert a complex number from rectangular form 'a + bi' to polar form, you first calculate its modulus as $r = \sqrt{a^2 + b^2}$ and its argument using $\theta = \tan^{-1}(\frac{b}{a})$. The polar form is then expressed as $r(\cos \theta + i \sin \theta)$. This transformation is useful because it simplifies multiplication and division of complex numbers; instead of dealing with individual components, you can multiply or divide their magnitudes and add or subtract their angles.
• Evaluate how understanding complex numbers in both rectangular and polar forms contributes to solving real-world problems in engineering and physics.
  • Understanding complex numbers in both rectangular and polar forms allows engineers and physicists to model and analyze phenomena that involve oscillations, waves, and electrical circuits. In engineering, for instance, alternating current (AC) circuits can be represented using phasors in polar form for efficient calculations of impedance and phase differences. In physics, wave functions in quantum mechanics often utilize complex numbers to represent probabilities. By applying both forms effectively, professionals can simplify computations while gaining deeper insights into dynamic systems.

Related terms

Imaginary Unit:

The imaginary unit, denoted as 'i', is defined as the square root of -1 and is used to define complex numbers.

Real Number: A real number is any value along the continuous number line, including rational and irrational numbers, but excluding imaginary numbers.

Polar Form: The polar form of a complex number expresses it in terms of its magnitude (or modulus) and angle (or argument) relative to the positive real axis.