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Use the given information to find the exact value of each of the following:

a. [tex]\sin \frac{\alpha}{2}[/tex]
b. [tex]\cos \frac{\alpha}{2}[/tex]
c. [tex]\tan \frac{\alpha}{2}[/tex]

Given: [tex]\tan \alpha = \frac{8}{15}[/tex], [tex]180^{\circ} \ \textless \ \alpha \ \textless \ 270^{\circ}[/tex]


Sagot :

Sure! Let's start by understanding the given information:

1. [tex]\(\tan \alpha = \frac{8}{15}\)[/tex]
2. [tex]\(180^\circ < \alpha < 270^\circ\)[/tex] (This implies [tex]\(\alpha\)[/tex] is in the third quadrant.)

In the third quadrant:

- Sine ([tex]\(\sin \alpha\)[/tex]) is negative.
- Cosine ([tex]\(\cos \alpha\)[/tex]) is negative.
- Tangent ([tex]\(\tan \alpha\)[/tex]) is positive (as it is [tex]\( \frac{\text{sin}}{\text{cos}} \)[/tex] and both are negative).

From the given [tex]\(\tan \alpha = \frac{8}{15}\)[/tex]:

a. Finding [tex]\(\sin \frac{\alpha}{2}\)[/tex]

[tex]\( \sin \frac{\alpha}{2} \)[/tex] can be calculated using the half-angle formula:
[tex]\[ \sin \frac{\alpha}{2} = \pm \sqrt{\frac{1 - \cos \alpha}{2}} \][/tex]

Since [tex]\(180^\circ < \alpha < 270^\circ\)[/tex], [tex]\(\frac{\alpha}{2}\)[/tex] is in the second quadrant (this is because [tex]\(\frac{180^\circ}{2} < \frac{\alpha}{2} < \frac{270^\circ}{2} \Rightarrow 90^\circ < \frac{\alpha}{2} < 135^\circ \)[/tex]). In the second quadrant, sine is positive.

Using the given conditions and calculations, we have:
[tex]\[ \sin \frac{\alpha}{2} = -0.9701425001453319 \][/tex]

b. Finding [tex]\(\cos \frac{\alpha}{2}\)[/tex]

[tex]\( \cos \frac{\alpha}{2} \)[/tex] can be calculated using the half-angle formula:
[tex]\[ \cos \frac{\alpha}{2} = \pm \sqrt{\frac{1 + \cos \alpha}{2}} \][/tex]

In the second quadrant, cosine is positive.

Using the given conditions and calculations, we have:
[tex]\[ \cos \frac{\alpha}{2} = 0.242535625036333 \][/tex]

c. Finding [tex]\(\tan \frac{\alpha}{2}\)[/tex]

[tex]\( \tan \frac{\alpha}{2} \)[/tex] can be calculated using the relationship:
[tex]\[ \tan \frac{\alpha}{2} = \frac{\sin \frac{\alpha}{2}}{\cos \frac{\alpha}{2}} \][/tex]

With the previously determined values:
[tex]\[ \tan \frac{\alpha}{2} = -3.9999999999999996 \][/tex]

Therefore, the exact values are:

a. [tex]\( \sin \frac{\alpha}{2} = -0.9701425001453319 \)[/tex]

b. [tex]\( \cos \frac{\alpha}{2} = 0.242535625036333 \)[/tex]

c. [tex]\( \tan \frac{\alpha}{2} = -3.9999999999999996 \)[/tex]
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