Math Problem Statement

Find all degree solutions for the following equation: cos(5θ) = 0. Additionally, solve for x in the interval 0 ≤ x < 2π when sec(3x) = -1.

Solution

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Problem 1:

Find all degree solutions for the following: cos(5θ)=0\cos(5\theta) = 0 Solution:

The cosine function equals zero at: θ=90+180k,kZ\theta = 90^\circ + 180^\circ k, \quad k \in \mathbb{Z}

Here, 5θ5\theta represents the argument: 5θ=90+180k5\theta = 90^\circ + 180^\circ k

Divide by 5 to isolate θ\theta: θ=905+180k5\theta = \frac{90^\circ}{5} + \frac{180^\circ k}{5}

Simplify: θ=18+36k,kZ\theta = 18^\circ + 36^\circ k, \quad k \in \mathbb{Z}

Since cosine is periodic, all solutions are represented by: θ=18+36kandθ=54+36k\theta = 18^\circ + 36^\circ k \quad \text{and} \quad \theta = 54^\circ + 36^\circ k


Problem 2:

Find all solutions if 0x<2π0 \leq x < 2\pi: sec(3x)=1\sec(3x) = -1

Solution:

Recall that sec(x)=1\sec(x) = -1 when cos(x)=1\cos(x) = -1. Therefore, we solve: cos(3x)=1\cos(3x) = -1

The cosine function equals 1-1 at: 3x=π+2nπ,nZ3x = \pi + 2n\pi, \quad n \in \mathbb{Z}

Simplify for xx by dividing by 3: x=π3+2nπ3,nZx = \frac{\pi}{3} + \frac{2n\pi}{3}, \quad n \in \mathbb{Z}

Find solutions in 0x<2π0 \leq x < 2\pi:

  1. x=π3x = \frac{\pi}{3}
  2. Add 2π/32\pi/3: x=π3+2π3=πx = \frac{\pi}{3} + \frac{2\pi}{3} = \pi
  3. Add another 2π/32\pi/3: x=π+2π3=5π3x = \pi + \frac{2\pi}{3} = \frac{5\pi}{3}

Thus, the solutions are: x=π3,π,5π3x = \frac{\pi}{3}, \pi, \frac{5\pi}{3}


Final Answers:

  1. Problem 1: θ=18+36kandθ=54+36k,kZ\theta = 18^\circ + 36^\circ k \quad \text{and} \quad \theta = 54^\circ + 36^\circ k, \quad k \in \mathbb{Z}
  2. Problem 2: x=π3,π,5π3x = \frac{\pi}{3}, \pi, \frac{5\pi}{3}

Would you like further details or explanations?


Related Questions:

  1. What are the general forms for sine and cosine equations for periodicity?
  2. How does the secant function relate to the cosine function?
  3. Can you calculate similar solutions for sine equations?
  4. What happens to the range of solutions if the domain changes?
  5. How do transformations like 5θ5\theta or 3x3x affect trigonometric functions?

Tip: Always simplify trigonometric identities to connect them with standard results like zeros of cosine and sine.

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Math Problem Analysis

Mathematical Concepts

Trigonometric Equations
Periodic Functions
Inverse Trigonometric Functions

Formulas

cos(θ) = 0 occurs at θ = 90° + 180°k, where k ∈ ℤ
sec(x) = -1 implies cos(x) = -1, and cos(x) = -1 at x = π + 2nπ, where n ∈ ℤ

Theorems

Periodic nature of cosine function
Relationship between secant and cosine

Suitable Grade Level

Grades 10-12