# De Moivre's theorem

De Moivre’s Theorem

Understanding De Moivre’s Theorem

• Know that De Moivre’s Theorem is a powerful tool that links trigonometry and complex numbers.
• Understand that the theorem states (cos θ + i sin θ)^n = cos nθ + i sin nθ where ‘i’ is the imaginary unit.
• Keep in mind that ‘θ’ is the argument and ‘n’ any real number.

Applying De Moivre’s Theorem

• Practice using the theorem to find powers and roots of complex numbers expressed in trigonometric form. This can simplify calculations significantly.
• Note that the theorem also helps in expanding trigonometric functions.
• Often used for demonstrating the trigonometric identities such as cos(nθ) and sin(nθ).

Working with Trigonometric Form

• Beware that complex numbers must first be written in trigonometric form i.e. cos θ + i sin θ before applying De Moivre’s Theorem.
• Pay attention to the signs and the direction of the angle when converting numbers into trigonometric form.
• Remember that cos θ represents the real part and sin θ the imaginary part of a complex number.

De Moivre’s Theorem and Roots of Complex Numbers

• To find nth roots of a complex number like z^1/n, use the inverse form of De Moivre’s Theorem.
• Here, ‘n’ is an integer and give rise to n distinct roots.
• Understand that these roots are equally spaced on a circle on the Argand diagram.

The Importance of De Moivre’s Theorem

• Emulate how the theorem is often used to tackle problems in physics, engineering, and computer science.
• Realize the theorem’s usefulness in manipulation of powers and roots of complex numbers, simplifying trigonometric identities, and simplifying computations in geometry.

By revising these points and practicing problems, you will solidify the comprehension of De Moivre’s Theorem and be equipped for its applications.