Math Problem Statement

cos(x-pi/6)>= -1/2

Solution

To solve the inequality cos(xπ6)12\cos(x - \frac{\pi}{6}) \geq -\frac{1}{2}, let's follow these steps:

Step 1: Solve the related equation

Start by solving the equation cos(xπ6)=12\cos(x - \frac{\pi}{6}) = -\frac{1}{2}.

We know that cos(θ)=12\cos(\theta) = -\frac{1}{2} at specific angles, namely: θ=2π3+2nπorθ=4π3+2nπ\theta = \frac{2\pi}{3} + 2n\pi \quad \text{or} \quad \theta = \frac{4\pi}{3} + 2n\pi for any integer nn.

Thus, for the equation cos(xπ6)=12\cos(x - \frac{\pi}{6}) = -\frac{1}{2}, we have: xπ6=2π3+2nπorxπ6=4π3+2nπx - \frac{\pi}{6} = \frac{2\pi}{3} + 2n\pi \quad \text{or} \quad x - \frac{\pi}{6} = \frac{4\pi}{3} + 2n\pi

Step 2: Solve for xx

Now solve these two equations for xx:

  1. xπ6=2π3+2nπx - \frac{\pi}{6} = \frac{2\pi}{3} + 2n\pi x=2π3+π6+2nπ=4π6+π6+2nπ=5π6+2nπx = \frac{2\pi}{3} + \frac{\pi}{6} + 2n\pi = \frac{4\pi}{6} + \frac{\pi}{6} + 2n\pi = \frac{5\pi}{6} + 2n\pi

  2. xπ6=4π3+2nπx - \frac{\pi}{6} = \frac{4\pi}{3} + 2n\pi x=4π3+π6+2nπ=8π6+π6+2nπ=9π6+2nπ=3π2+2nπx = \frac{4\pi}{3} + \frac{\pi}{6} + 2n\pi = \frac{8\pi}{6} + \frac{\pi}{6} + 2n\pi = \frac{9\pi}{6} + 2n\pi = \frac{3\pi}{2} + 2n\pi

Thus, the solutions to the equation cos(xπ6)=12\cos(x - \frac{\pi}{6}) = -\frac{1}{2} are: x=5π6+2nπorx=3π2+2nπx = \frac{5\pi}{6} + 2n\pi \quad \text{or} \quad x = \frac{3\pi}{2} + 2n\pi

Step 3: Analyze the inequality

The inequality cos(xπ6)12\cos(x - \frac{\pi}{6}) \geq -\frac{1}{2} means xπ6x - \frac{\pi}{6} must be within the range of angles where cos(θ)\cos(\theta) is greater than or equal to 12-\frac{1}{2}.

For cos(θ)12\cos(\theta) \geq -\frac{1}{2}, the angles θ\theta are within the range: π3θ5π3-\frac{\pi}{3} \leq \theta \leq \frac{5\pi}{3} This corresponds to the interval for xπ6x - \frac{\pi}{6}. So, we must solve: π3xπ65π3-\frac{\pi}{3} \leq x - \frac{\pi}{6} \leq \frac{5\pi}{3}

Step 4: Adjust for xx

Add π6\frac{\pi}{6} to each part of the inequality: π3+π6x5π3+π6-\frac{\pi}{3} + \frac{\pi}{6} \leq x \leq \frac{5\pi}{3} + \frac{\pi}{6} Simplifying: 2π6+π6=π6,5π3+π6=10π6+π6=11π6-\frac{2\pi}{6} + \frac{\pi}{6} = -\frac{\pi}{6}, \quad \frac{5\pi}{3} + \frac{\pi}{6} = \frac{10\pi}{6} + \frac{\pi}{6} = \frac{11\pi}{6}

Thus, the inequality becomes: π6x11π6-\frac{\pi}{6} \leq x \leq \frac{11\pi}{6}

Step 5: General Solution

The general solution is the set of all xx values such that: π6x11π6+2nπ-\frac{\pi}{6} \leq x \leq \frac{11\pi}{6} + 2n\pi where nn is any integer, since the cosine function has a period of 2π2\pi.

Final Answer:

The solution to the inequality cos(xπ6)12\cos(x - \frac{\pi}{6}) \geq -\frac{1}{2} is: x[π6,11π6]+2nπ,nZx \in \left[ -\frac{\pi}{6}, \frac{11\pi}{6} \right] + 2n\pi, \quad n \in \mathbb{Z}


Would you like any additional details or clarifications?

Related Questions:

  1. How would the solution change if the inequality was cos(xπ6)12\cos(x - \frac{\pi}{6}) \leq -\frac{1}{2}?
  2. How can you graph the function y=cos(xπ6)y = \cos(x - \frac{\pi}{6}) to visualize this inequality?
  3. What other trigonometric inequalities are commonly solved in similar ways?
  4. How can you apply this solution to real-world problems?
  5. How does shifting the cosine function affect the solution to the inequality?

Tip:

When solving trigonometric inequalities, always consider the periodic nature of the functions and adjust the range of solutions accordingly by adding multiples of the period.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Inequalities
Cosine Function
Periodic Functions

Formulas

cos(θ) = -1/2
x - pi/6 = 2pi/3 + 2npi
x - pi/6 = 4pi/3 + 2npi

Theorems

Cosine Function Properties
Trigonometric Inequalities

Suitable Grade Level

Grades 10-12