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Given that [tex]$\cos (\theta)=\frac{\sqrt{2}}{2}$[/tex] and [tex]$\frac{3 \pi}{2}\ \textless \ \theta\ \textless \ 2 \pi$[/tex], evaluate [tex]$\sin (\theta)$[/tex] and [tex]$\tan (\theta)$[/tex].

[tex]$\sin (\theta)=$[/tex] ?

[tex]$\tan (\theta)=$[/tex] ?

A. [tex]$-\sqrt{2}$[/tex]

B. [tex]$-\frac{\sqrt{2}}{2}$[/tex]

C. [tex]$\frac{\sqrt{2}}{2}$[/tex]

D. [tex]$\sqrt{2}$[/tex]


Sagot :

Let's solve for [tex]\(\sin(\theta)\)[/tex] and [tex]\(\tan(\theta)\)[/tex] given that [tex]\(\cos(\theta) = \frac{\sqrt{2}}{2}\)[/tex] and [tex]\(\frac{3\pi}{2} < \theta < 2\pi\)[/tex].

### Step-by-Step Solution:

1. Identify the Quadrant:
Given that [tex]\(\frac{3\pi}{2} < \theta < 2\pi\)[/tex], we know that [tex]\(\theta\)[/tex] is in the fourth quadrant.

2. Determine [tex]\(\theta\)[/tex]:
In the fourth quadrant, [tex]\(\cos(\theta) = \frac{\sqrt{2}}{2}\)[/tex] corresponds to an angle of [tex]\(\theta = \frac{7\pi}{4}\)[/tex]. This angle satisfies the given range because [tex]\( \frac{7\pi}{4} \)[/tex] (which is [tex]\(315^\circ\)[/tex]) is between [tex]\( 270^\circ (\frac{3\pi}{2}) \)[/tex] and [tex]\( 360^\circ (2\pi) \)[/tex].

3. Calculate [tex]\(\sin(\theta)\)[/tex]:
In the fourth quadrant, the sine function is negative. The value [tex]\(\theta = \frac{7\pi}{4}\)[/tex] corresponds to an angle where sine value is:
[tex]\[ \sin\left(\frac{7\pi}{4}\right) = -\frac{\sqrt{2}}{2} \][/tex]

4. Calculate [tex]\(\tan(\theta)\)[/tex]:
The tangent function is the ratio of sine and cosine:
[tex]\[ \tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)} \][/tex]
Given [tex]\(\sin(\theta) = -\frac{\sqrt{2}}{2}\)[/tex] and [tex]\(\cos(\theta) = \frac{\sqrt{2}}{2}\)[/tex]:
[tex]\[ \tan\left(\frac{7\pi}{4}\right) = \frac{-\frac{\sqrt{2}}{2}}{\frac{\sqrt{2}}{2}} = -1 \][/tex]

### Conclusion:
- [tex]\(\sin(\theta) = -\frac{\sqrt{2}}{2}\)[/tex]
- [tex]\(\tan(\theta) = -1\)[/tex]

Thus, the numerical values are:
- [tex]\(\sin(\theta) = -0.7071067811865477\)[/tex]
- [tex]\(\tan(\theta) = -1.0000000000000004\)[/tex]

Answer:

For [tex]\(\cos(\theta) = \frac{\sqrt{2}}{2}\)[/tex] and [tex]\(\frac{3\pi}{2} < \theta < 2\pi\)[/tex]:

[tex]\(\sin(\theta) = -\frac{\sqrt{2}}{2}\)[/tex]

[tex]\(\tan(\theta) = -1\)[/tex]