Math Problem Statement

Let θ be an angle in quadrant III such that sin θ = -3/5. Find the exact values of sec θ and cot θ.

Solution

We are given that sinθ=35\sin \theta = -\frac{3}{5} and that θ\theta is in quadrant III, where both sine and cosine are negative. We need to find the exact values of secθ\sec \theta and cotθ\cot \theta.

Step 1: Find cosθ\cos \theta

Using the Pythagorean identity: sin2θ+cos2θ=1\sin^2 \theta + \cos^2 \theta = 1 Substitute sinθ=35\sin \theta = -\frac{3}{5}: (35)2+cos2θ=1\left( -\frac{3}{5} \right)^2 + \cos^2 \theta = 1 925+cos2θ=1\frac{9}{25} + \cos^2 \theta = 1 cos2θ=1925=1625\cos^2 \theta = 1 - \frac{9}{25} = \frac{16}{25} cosθ=45\cos \theta = -\frac{4}{5} (We take the negative root because θ\theta is in quadrant III, where cosine is negative.)

Step 2: Find secθ\sec \theta

secθ=1cosθ=145=54\sec \theta = \frac{1}{\cos \theta} = \frac{1}{-\frac{4}{5}} = -\frac{5}{4}

Step 3: Find cotθ\cot \theta

Using the identity cotθ=cosθsinθ\cot \theta = \frac{\cos \theta}{\sin \theta}: cotθ=4535=43\cot \theta = \frac{-\frac{4}{5}}{-\frac{3}{5}} = \frac{4}{3}

Final Answers:

  • secθ=54\sec \theta = -\frac{5}{4}
  • cotθ=43\cot \theta = \frac{4}{3}

Would you like more details on any step, or do you have questions?

Here are 5 related questions:

  1. How do you determine the signs of trigonometric functions in different quadrants?
  2. What is the significance of using the Pythagorean identity in trigonometry?
  3. Can you explain how to derive secθ\sec \theta from cosθ\cos \theta?
  4. How does the quadrant affect the value of cotθ\cot \theta?
  5. What other identities can be used to calculate secant and cotangent?

Tip: Remember that in quadrant III, both sine and cosine are negative, while tangent and cotangent are positive.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Quadrants

Formulas

sin² θ + cos² θ = 1
sec θ = 1/cos θ
cot θ = cos θ/sin θ

Theorems

Pythagorean Identity

Suitable Grade Level

Grades 10-12