Precalculus Examples

$7 - 2 i$

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 $a = 7$ and $b = - 2$ .

$| z | = \sqrt{{(- 2)}^{2} + 7^{2}}$

Step 4

Find $| z |$ .

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Step 4.1

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

$| z | = \sqrt{4 + 7^{2}}$

Step 4.2

Raise $7$ to the power of $2$ .

$| z | = \sqrt{4 + 49}$

Step 4.3

Add $4$ and $49$ .

$| z | = \sqrt{53}$

Step 5

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

$θ = \arctan (\frac{- 2}{7})$

Step 6

Since inverse tangent of $\frac{- 2}{7}$ produces an angle in the fourth quadrant, the value of the angle is $- 0.27829965$ .

$θ = - 0.27829965$

Step 7

Substitute the values of $θ = - 0.27829965$ and $| z | = \sqrt{53}$ .

$\sqrt{53} (\cos (- 0.27829965) + i \sin (- 0.27829965))$