Math Problem Statement

Find all solutions in the interval [0, 2π] for the equation cos(2x) − √3 sin(x) = 1.

Solution

The equation given is:

cos(2x)3sin(x)=1\cos(2x) - \sqrt{3} \sin(x) = 1

We are tasked with finding all solutions for xx in the interval [0,2π][0, 2\pi].

Step-by-step solution:

  1. Rearrange the equation:

    cos(2x)=1+3sin(x)\cos(2x) = 1 + \sqrt{3} \sin(x)

  2. Substitute cos(2x)\cos(2x) using a double-angle identity: Recall that cos(2x)\cos(2x) can be expressed as:

    cos(2x)=12sin2(x)\cos(2x) = 1 - 2\sin^2(x)

    Substituting this into the equation:

    12sin2(x)=1+3sin(x)1 - 2\sin^2(x) = 1 + \sqrt{3} \sin(x)

  3. Simplify the equation: First, subtract 1 from both sides:

    2sin2(x)=3sin(x)-2\sin^2(x) = \sqrt{3}\sin(x)

    Divide by 1-1 to simplify further:

    2sin2(x)=3sin(x)2\sin^2(x) = -\sqrt{3} \sin(x)

  4. Factor the equation: Move all terms to one side to set the equation to zero:

    2sin2(x)+3sin(x)=02\sin^2(x) + \sqrt{3}\sin(x) = 0

    Factor out sin(x)\sin(x):

    sin(x)(2sin(x)+3)=0\sin(x)(2\sin(x) + \sqrt{3}) = 0

  5. Solve each factor: Now, we have two cases:

    • Case 1: sin(x)=0\sin(x) = 0

      The solutions are x=0,π,2πx = 0, \pi, 2\pi.

    • Case 2: 2sin(x)+3=02\sin(x) + \sqrt{3} = 0

      Solve for sin(x)\sin(x):

      2sin(x)=32\sin(x) = -\sqrt{3} sin(x)=32\sin(x) = -\frac{\sqrt{3}}{2}

      The solutions for sin(x)=32\sin(x) = -\frac{\sqrt{3}}{2} in the interval [0,2π][0, 2\pi] are:

      x=4π3,5π3x = \frac{4\pi}{3}, \frac{5\pi}{3}

Final answer:

The solutions in the interval [0,2π][0, 2\pi] are:

x=0,π,2π,4π3,5π3x = 0, \pi, 2\pi, \frac{4\pi}{3}, \frac{5\pi}{3}

Would you like further details or explanations for any of the steps?


Here are 5 related questions to consider:

  1. What are the common trigonometric identities used to simplify trigonometric equations?
  2. How does the double-angle identity for cosine help in solving equations like this?
  3. Can you explain how factoring helps in solving quadratic trigonometric equations?
  4. What is the significance of the interval [0,2π][0, 2\pi] when finding solutions?
  5. How do you determine solutions for sine or cosine in different quadrants?

Tip: Always look for opportunities to apply trigonometric identities when working with equations involving multiple angles (like 2x2x or 3x3x).

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Equation Solving
Double-Angle Identity
Factoring

Formulas

cos(2x) = 1 - 2sin^2(x)
sin(x) = -√3/2

Theorems

Trigonometric Identities
Double-Angle Identity for Cosine

Suitable Grade Level

Grades 11-12