Precalculus Examples

$20 \sqrt{3} - 20 i$

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 $a = 20 \sqrt{3}$ and $b = - 20$ .

$| z | = \sqrt{{(- 20)}^{2} + {(20 \sqrt{3})}^{2}}$

Step 4

Find $| z |$ .

Tap for more steps...

Step 4.1

Simplify the expression.

Tap for more steps...

Step 4.1.1

Raise $- 20$ to the power of $2$ .

$| z | = \sqrt{400 + {(20 \sqrt{3})}^{2}}$

Step 4.1.2

Apply the product rule to $20 \sqrt{3}$ .

$| z | = \sqrt{400 + 20^{2} {\sqrt{3}}^{2}}$

Step 4.1.3

Raise $20$ to the power of $2$ .

$| z | = \sqrt{400 + 400 {\sqrt{3}}^{2}}$

Step 4.2

Rewrite ${\sqrt{3}}^{2}$ as $3$ .

Tap for more steps...

Step 4.2.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{3}$ as $3^{\frac{1}{2}}$ .

$| z | = \sqrt{400 + 400 {(3^{\frac{1}{2}})}^{2}}$

Step 4.2.2

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$| z | = \sqrt{400 + 400 \cdot 3^{\frac{1}{2} \cdot 2}}$

Step 4.2.3

Combine $\frac{1}{2}$ and $2$ .

$| z | = \sqrt{400 + 400 \cdot 3^{\frac{2}{2}}}$

Step 4.2.4

Cancel the common factor of $2$ .

Tap for more steps...

Step 4.2.4.1

Cancel the common factor.

$| z | = \sqrt{400 + 400 \cdot 3^{\frac{2}{2}}}$

Step 4.2.4.2

Rewrite the expression.

$| z | = \sqrt{400 + 400 \cdot 3}$

Step 4.2.5

Evaluate the exponent.

$| z | = \sqrt{400 + 400 \cdot 3}$

Step 4.3

Simplify the expression.

Tap for more steps...

Step 4.3.1

Multiply $400$ by $3$ .

$| z | = \sqrt{400 + 1200}$

Step 4.3.2

Add $400$ and $1200$ .

$| z | = \sqrt{1600}$

Step 4.3.3

Rewrite $1600$ as $40^{2}$ .

$| z | = \sqrt{40^{2}}$

Step 4.3.4

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

$| z | = 40$

Step 5

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

$θ = \arctan (\frac{- 20}{20 \sqrt{3}})$

Step 6

Since inverse tangent of $\frac{- 20}{20 \sqrt{3}}$ produces an angle in the fourth quadrant, the value of the angle is $- \frac{π}{6}$ .

$θ = - \frac{π}{6}$

Step 7

Substitute the values of $θ = - \frac{π}{6}$ and $| z | = 40$ .

$40 (\cos (- \frac{π}{6}) + i \sin (- \frac{π}{6}))$