Given that cosθ=108⎯⎯⎯⎯⎯⎯√12 and cotθ is negative, determine θ and cotθ. Enter the angle θ in degrees from the interval [0°,360°). Write the exact answer. Do not round.

Respuesta :

The question is an illustration of trigonometry identity

The value of [tex]\theta[/tex] is [tex]337.38^o[/tex] and [tex]\cot(\theta) = -\frac{12}{5}[/tex]

The question is a not clear, so I will make use of [tex]\cos \theta = \frac{12}{13}[/tex].

Using:

[tex]\sin^2 \theta + \cos^2 \theta = 1[/tex]

Substitute [tex]\cos \theta = \frac{12}{13}[/tex]

[tex]\sin^2 \theta + (\frac{12}{13})^2 = 1[/tex]

Collect like terms

[tex]\sin^2 \theta = 1- (\frac{12}{13})^2[/tex]

[tex]\sin^2 \theta = 1- \frac{144}{169}[/tex]

Take LCM

[tex]\sin^2 \theta = \frac{169 - 144}{169}[/tex]

[tex]\sin^2 \theta = \frac{25}{169}[/tex]

Take square roots

[tex]\sin \theta = \±\frac{5}{13}[/tex]

From the question, we have cosine to be positive and [tex]\cot \theta < 0[/tex]

This means that [tex]\theta[/tex] is in the fourth quadrant, where [tex]\sin(\theta) < 0[/tex]

So, we have:

[tex]\sin \theta = -\frac{5}{13}[/tex]

The value of [tex]\cot(\theta)[/tex] is the

[tex]\cot(\theta) = \frac{\cos(\theta)}{\sin(\theta)}[/tex]

Substitute [tex]\sin \theta = -\frac{5}{13}[/tex] and [tex]\cos \theta = \frac{12}{13}[/tex]

[tex]\cot(\theta) = \frac{12}{13} \div -\frac{5}{13}[/tex]

Rewrite as:

[tex]\cot(\theta) = \frac{12}{13} \times -\frac{13}{5}[/tex]

[tex]\cot(\theta) = -\frac{12}{5}[/tex]

The value of [tex]\theta[/tex] is calculated as follows:

[tex]\sin \theta = -\frac{5}{13}[/tex]

Take arcsin of both sides

[tex]\theta = sin^{-1}(-5/13)[/tex]

Because [tex]\theta[/tex] is in the 4th quadrant, the above equation becomes

[tex]\theta = 360^o + sin^{-1}(-5/13)[/tex]

[tex]\theta = 360^o - 22.62^o[/tex]

[tex]\theta = 337.38^o[/tex]

Hence, the value of [tex]\theta[/tex] is [tex]337.38^o[/tex] and [tex]\cot(\theta) = -\frac{12}{5}[/tex]

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