Trigonometry Examples

$z = 5 i$

Step 1

This is the trigonometric form of a complex number where $| z |$ is the modulus and $θ$ is the angle created on the complex plane.

$z = a + b i = | z | (\cos (θ) + i \sin (θ))$

Step 2

The modulus of a complex number is the distance from the origin on the complex plane.

$| z | = \sqrt{a^{2} + b^{2}}$ where $z = a + b i$

Step 3

Substitute the actual values of $a = 0$ and $b = 5$ .

$| z | = \sqrt{5^{2}}$

Step 4

Pull terms out from under the radical, assuming positive real numbers.

$| z | = 5$

Step 5

The angle of the point on the complex plane is the inverse tangent of the complex portion over the real portion.

$θ = \arctan (\frac{5}{0})$

Step 6

Since the argument is undefined and $b$ is positive, the angle of the point on the complex plane is $\frac{π}{2}$ .

$θ = \frac{π}{2}$

Step 7

Substitute the values of $θ = \frac{π}{2}$ and $| z | = 5$ .

$5 (\cos (\frac{π}{2}) + i \sin (\frac{π}{2}))$

Step 8

Replace the right side of the equation with the trigonometric form.

$z = 5 (\cos (\frac{π}{2}) + i \sin (\frac{π}{2}))$