# Precalculus : Polar Form of Complex Numbers

## Example Questions

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### Example Question #3 : Express Complex Numbers In Polar Form

Express the complex number  in polar form.

Possible Answers:

Correct answer:

Explanation:

The figure below shows a complex number plotted on the complex plane. The horizontal axis is the real axis and the vertical axis is the imaginary axis.

The polar form of a complex number is . We want to find the real and complex components in terms of  and  where  is the length of the vector and  is the angle made with the real axis.

We use the Pythagorean Theorem to find :

We find  by solving the trigonometric ratio

Using ,

Then we plug  and  into our polar equation to obtain

### Example Question #4 : Express Complex Numbers In Polar Form

What is the polar form of the complex number  ?

Possible Answers:

Correct answer:

Explanation:

The correct answer is

The polar form of a complex number  is  where  is the modulus of the complex number and  is the angle in radians between the real axis and the line that passes through  (   and ). We can solve for  and  easily for the complex number :

which gives us

### Example Question #1 : Express Complex Numbers In Polar Form

Express the complex number in polar form:

Possible Answers:

Correct answer:

Explanation:

Remember that the standard form of a complex number is: , which can be rewritten in polar form as: .

To find r, we must find the length of the line  by using the Pythagorean theorem:

To find , we can use the equation

Note that this value is in radians, NOT degrees.

Thus, the polar form of this equation can be written as

### Example Question #6 : Express Complex Numbers In Polar Form

Express this complex number in polar form.

Possible Answers:

None of these answers are correct.

Correct answer:

Explanation:

Given these identities, first solve for  and . The polar form of a complex number is:

at  (because the original point, (1,1) is in Quadrant 1)

Therefore...

### Example Question #1 : Express Complex Numbers In Polar Form

Convert to polar form:

Possible Answers:

Correct answer:

Explanation:

First, find the radius :

Then find the angle, thinking of the imaginary part as the height and the radius as the hypotenuse of a right triangle:

according to the calculator.

We can get the positive coterminal angle by adding :

The polar form is

### Example Question #8 : Express Complex Numbers In Polar Form

Convert to polar form:

Possible Answers:

Correct answer:

Explanation:

First find the radius, :

Now find the angle, thinking of the imaginary part as the height and the radius as the hypotenuse of a right triangle:

according to the calculator.

This is an appropriate angle to stay with since this number should be in quadrant I.

The complex number in polar form is

### Example Question #9 : Express Complex Numbers In Polar Form

Convert the complex number to polar form

Possible Answers:

Correct answer:

Explanation:

First find :

Now find the angle. Consider the imaginary part to be the height of a right triangle with hypotenuse .

according to the calculator.

What the calculator does not know is that this angle is actually located in quadrant II, since the real part is negative and the imaginary part is positive.

To find the angle in quadrant II whose sine is also , subtract from :

The complex number in polar form is

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