Find one positive and one negative angle coterminal with an angle of [tex]\frac{9 \pi}{6}[/tex].

A. [tex]\frac{11 \pi}{6} ; \frac{-7 \pi}{6}[/tex]
B. [tex]\frac{3 \pi}{6} ; \frac{-21 \pi}{6}[/tex]
C. [tex]\frac{21 \pi}{6} ; \frac{-3 \pi}{6}[/tex]
D. [tex]\frac{7 \pi}{6} ; \frac{-11 \pi}{6}[/tex]



Answer :

To find coterminal angles with a given angle, we can add or subtract multiples of [tex]\(2\pi\)[/tex]. This is because [tex]\(2\pi\)[/tex] radians represent a full rotation, and adding or subtracting full rotations will result in an angle that points in the same direction (i.e., coterminal).

Given the angle is [tex]\(\frac{9\pi}{6}\)[/tex], we can simplify it first if possible:

[tex]\[ \frac{9\pi}{6} = \frac{3 \cdot 3 \pi}{3 \cdot 2} = \frac{3\pi}{2} \][/tex]

We need to find one positive and one negative coterminal angle with [tex]\(\frac{3\pi}{2}\)[/tex].

### Finding a Positive Coterminal Angle:

To find the positive coterminal angle, we add [tex]\(2\pi\)[/tex] to [tex]\(\frac{3\pi}{2}\)[/tex]:

[tex]\[ \frac{3\pi}{2} + 2\pi = \frac{3\pi}{2} + \frac{4\pi}{2} = \frac{7\pi}{2} \][/tex]

Now let's divide both parts by [tex]\(\pi\)[/tex] to simplify:

[tex]\[ \frac{7\pi}{2\pi} = 3.5 \][/tex]

This step confirms that our calculated result is [tex]\(3.5\)[/tex].

### Finding a Negative Coterminal Angle:

To find the negative coterminal angle, we subtract [tex]\(2\pi\)[/tex] from [tex]\(\frac{3\pi}{2}\)[/tex]:

[tex]\[ \frac{3\pi}{2} - 2\pi = \frac{3\pi}{2} - \frac{4\pi}{2} = \frac{-\pi}{2} \][/tex]

Now let's divide both parts by [tex]\(\pi\)[/tex] to simplify:

[tex]\[ \frac{-\pi}{2\pi} = -0.5 \][/tex]

This step confirms that our calculated result is [tex]\(-0.5\)[/tex].

Ultimately, the angles we have found are:

One positive coterminal angle: [tex]\(3.5\)[/tex]
One negative coterminal angle: [tex]\(-0.5\)[/tex]

Comparing this with the provided multiple-choice options, we see that none of the given answer choices perfectly matches our derived result of [tex]\(3.5\)[/tex] and [tex]\(-0.5\)[/tex]. However, based on the closest values available in the choices provided and given instructions, the correct analogical process guides to the values which essentially appreciate the nature of coterminal angles.

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