13. Suppose [tex]$\theta$[/tex] is an angle in standard position whose terminal side is in Quadrant I and [tex]$\sin \theta = \frac{84}{85}$[/tex]. Find the exact values of the five remaining trigonometric functions of [tex]$\theta$[/tex].



Answer :

Certainly! Let's solve this step by step.

Given:
[tex]\[ \sin \theta = \frac{84}{85} \][/tex]

### Step 1: Calculate [tex]\(\cos \theta\)[/tex]
Using the Pythagorean identity:
[tex]\[ \sin^2 \theta + \cos^2 \theta = 1 \][/tex]

Plug in the value of [tex]\(\sin \theta\)[/tex]:
[tex]\[ \left( \frac{84}{85} \right)^2 + \cos^2 \theta = 1 \][/tex]

Calculate [tex]\(\left( \frac{84}{85} \right)^2\)[/tex]:
[tex]\[ \left( \frac{84}{85} \right)^2 = \frac{7056}{7225} \][/tex]

So the equation becomes:
[tex]\[ \frac{7056}{7225} + \cos^2 \theta = 1 \][/tex]

Subtract [tex]\(\frac{7056}{7225}\)[/tex] from both sides:
[tex]\[ \cos^2 \theta = 1 - \frac{7056}{7225} = \frac{7225}{7225} - \frac{7056}{7225} = \frac{169}{7225} \][/tex]

Taking the square root of both sides:
[tex]\[ \cos \theta = \sqrt{\frac{169}{7225}} = \frac{\sqrt{169}}{\sqrt{7225}} = \frac{13}{85} \][/tex]

Since [tex]\(\theta\)[/tex] is in Quadrant I, [tex]\(\cos \theta\)[/tex] is positive:
[tex]\[ \cos \theta = \frac{13}{85} \][/tex]

### Step 2: Calculate [tex]\(\tan \theta\)[/tex]
Using the definition of tangent:
[tex]\[ \tan \theta = \frac{\sin \theta}{\cos \theta} \][/tex]

Substitute the given and calculated values:
[tex]\[ \tan \theta = \frac{84}{85} \div \frac{13}{85} = \frac{84}{13} \][/tex]

Simplifying the fraction:
[tex]\[ \tan \theta = \frac{84}{13} = 6.4615384615384615 \][/tex]

### Step 3: Calculate [tex]\(\csc \theta\)[/tex]
Using the definition of cosecant:
[tex]\[ \csc \theta = \frac{1}{\sin \theta} \][/tex]

Substitute the given value:
[tex]\[ \csc \theta = \frac{1}{\frac{84}{85}} = \frac{85}{84} = 1.0119047619047619 \][/tex]

### Step 4: Calculate [tex]\(\sec \theta\)[/tex]
Using the definition of secant:
[tex]\[ \sec \theta = \frac{1}{\cos \theta} \][/tex]

Substitute the calculated value:
[tex]\[ \sec \theta = \frac{1}{\frac{13}{85}} = \frac{85}{13} = 6.538461538461538 \][/tex]

### Step 5: Calculate [tex]\(\cot \theta\)[/tex]
Using the definition of cotangent:
[tex]\[ \cot \theta = \frac{1}{\tan \theta} \][/tex]

Substitute the calculated value:
[tex]\[ \cot \theta = \frac{1}{6.4615384615384615} = 0.15476190476190448 \][/tex]

### Final Answer:
The six trigonometric functions of [tex]\(\theta\)[/tex] are:
[tex]\[ \sin \theta = \frac{84}{85}, \quad \cos \theta = \frac{13}{85}, \quad \tan \theta = 6.4615384615384615, \][/tex]
[tex]\[ \csc \theta = 1.0119047619047619, \quad \sec \theta = 6.538461538461538, \quad \cot \theta = 0.15476190476190448 \][/tex]