Precalculus Examples

$- 2 \sqrt{2} + 2 i \sqrt{2}$

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 $a = - 2 \sqrt{2}$ and $b = 2 \sqrt{2}$ .

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

Step 4

Find $| z |$ .

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Step 4.1

Simplify the expression.

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Step 4.1.1

Apply the product rule to $2 \sqrt{2}$ .

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

Step 4.1.2

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

$| z | = \sqrt{4 {\sqrt{2}}^{2} + {(- 2 \sqrt{2})}^{2}}$

Step 4.2

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

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Step 4.2.1

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

$| z | = \sqrt{4 {(2^{\frac{1}{2}})}^{2} + {(- 2 \sqrt{2})}^{2}}$

Step 4.2.2

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

$| z | = \sqrt{4 \cdot 2^{\frac{1}{2} \cdot 2} + {(- 2 \sqrt{2})}^{2}}$

Step 4.2.3

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

$| z | = \sqrt{4 \cdot 2^{\frac{2}{2}} + {(- 2 \sqrt{2})}^{2}}$

Step 4.2.4

Cancel the common factor of $2$ .

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Step 4.2.4.1

Cancel the common factor.

$| z | = \sqrt{4 \cdot 2^{\frac{2}{2}} + {(- 2 \sqrt{2})}^{2}}$

Step 4.2.4.2

Rewrite the expression.

$| z | = \sqrt{4 \cdot 2 + {(- 2 \sqrt{2})}^{2}}$

Step 4.2.5

Evaluate the exponent.

$| z | = \sqrt{4 \cdot 2 + {(- 2 \sqrt{2})}^{2}}$

Step 4.3

Simplify the expression.

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Step 4.3.1

Multiply $4$ by $2$ .

$| z | = \sqrt{8 + {(- 2 \sqrt{2})}^{2}}$

Step 4.3.2

Apply the product rule to $- 2 \sqrt{2}$ .

$| z | = \sqrt{8 + {(- 2)}^{2} {\sqrt{2}}^{2}}$

Step 4.3.3

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

$| z | = \sqrt{8 + 4 {\sqrt{2}}^{2}}$

Step 4.4

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

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Step 4.4.1

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

$| z | = \sqrt{8 + 4 {(2^{\frac{1}{2}})}^{2}}$

Step 4.4.2

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

$| z | = \sqrt{8 + 4 \cdot 2^{\frac{1}{2} \cdot 2}}$

Step 4.4.3

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

$| z | = \sqrt{8 + 4 \cdot 2^{\frac{2}{2}}}$

Step 4.4.4

Cancel the common factor of $2$ .

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Step 4.4.4.1

Cancel the common factor.

$| z | = \sqrt{8 + 4 \cdot 2^{\frac{2}{2}}}$

Step 4.4.4.2

Rewrite the expression.

$| z | = \sqrt{8 + 4 \cdot 2}$

Step 4.4.5

Evaluate the exponent.

$| z | = \sqrt{8 + 4 \cdot 2}$

Step 4.5

Simplify the expression.

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Step 4.5.1

Multiply $4$ by $2$ .

$| z | = \sqrt{8 + 8}$

Step 4.5.2

Add $8$ and $8$ .

$| z | = \sqrt{16}$

Step 4.5.3

Rewrite $16$ as $4^{2}$ .

$| z | = \sqrt{4^{2}}$

Step 4.5.4

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

$| z | = 4$

Step 5

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

$θ = \arctan (\frac{2 \sqrt{2}}{- 2 \sqrt{2}})$

Step 6

Since inverse tangent of $\frac{2 \sqrt{2}}{- 2 \sqrt{2}}$ produces an angle in the second quadrant, the value of the angle is $\frac{3 π}{4}$ .

$θ = \frac{3 π}{4}$

Step 7

Substitute the values of $θ = \frac{3 π}{4}$ and $| z | = 4$ .

$4 (\cos (\frac{3 π}{4}) + i \sin (\frac{3 π}{4}))$