Questions: Determine a general formula (or formulas) for the solution to the following equation. Then, determine the specific solutions (if any) on the interval [0,2 π ).
cos θ+2 cos^2 θ=0
Describe in the most concise way possible the general solution to the given equation, where k is any integer. Select the correct choice below and fill in all the answer boxes within your choice. (Simplify your answers. Type any angle measures in radians. Use the smallest non-negative angle possible when describing the general form of each angle. Use ascending order, entering the expression based on the smallest angle first. Type exact answers, using π as needed. Use integers or fractions for any numbers in the expressions.) A. θ= + k B. θ= + k or θ= + k C. θ= + k or θ= + k or θ= + k D. θ= + k or θ= + k or θ= + k or θ= + k E. There is no solution.
Transcript text: Determine a general formula (or formulas) for the solution to the following equation. Then, determine the specific solutions (if any) on the interval $[0,2 \pi$ ).
\[
\cos \theta+2 \cos ^{2} \theta=0
\]
Describe in the most concise way possible the general solution to the given equation, where k is any integer. Select the correct choice below and fill in all the answer boxes within your choice.
(Simplify your answers. Type any angle measures in radians. Use the smallest non-negative angle possible when describing the general form of each angle. Use ascending order, entering the expression based on the smallest angle first. Type exact answers, using $\pi$ as needed. Use integers or fractions for any numbers in the expressions.)
A. $\theta=$ $\square$ $+$ k
B. $\theta=$ $\square$ $+\square$ k or $\theta=$ $\square$ $+$ k
C. $\theta=$ $\square$ $+$ $\square$ k or $\theta=$ $\square$ $+$ $\square$ $k$ or $\theta=$ $\square$ $+$ k
D. $\theta=$ $\square$ $+$ $k$ or $\theta=$ $\square$ $+\square$
$\square$ $k$ or $\theta=$ $\square$ $+$ $k$ or $\theta=$ $\square$ $+\square$ k
E. There is no solution.
Solution
Solution Steps
To solve the equation \(\cos \theta + 2 \cos^2 \theta = 0\), we can start by factoring the equation. This involves recognizing that it can be rewritten in a form that allows us to use the zero-product property. Once factored, we can solve for \(\theta\) by finding the angles that satisfy each factor. Finally, we determine the specific solutions within the interval \([0, 2\pi]\).
Step 1: Rewrite the Equation
We start with the equation:
\[
\cos \theta + 2 \cos^2 \theta = 0
\]
This can be factored as:
\[
\cos \theta (1 + 2 \cos \theta) = 0
\]
Step 2: Solve Each Factor
From the factored equation, we have two cases to solve:
\(\cos \theta = 0\)
\(1 + 2 \cos \theta = 0\)
Case 1: \(\cos \theta = 0\)
The solutions for \(\cos \theta = 0\) are:
\[
\theta = \frac{\pi}{2} + k\pi \quad \text{for any integer } k
\]
Within the interval \([0, 2\pi]\), the specific solutions are:
\[
\theta = \frac{\pi}{2} \quad \text{and} \quad \theta = \frac{3\pi}{2}
\]
Case 2: \(1 + 2 \cos \theta = 0\)
Rearranging gives:
\[
\cos \theta = -\frac{1}{2}
\]
The solutions for \(\cos \theta = -\frac{1}{2}\) are:
\[
\theta = \frac{2\pi}{3} + 2k\pi \quad \text{and} \quad \theta = \frac{4\pi}{3} + 2k\pi \quad \text{for any integer } k
\]
Within the interval \([0, 2\pi]\), the specific solutions are:
\[
\theta = \frac{2\pi}{3} \quad \text{and} \quad \theta = \frac{4\pi}{3}
\]
Step 3: Compile All Solutions
Combining all specific solutions from both cases, we have:
\[
\theta = \frac{\pi}{2}, \frac{2\pi}{3}, \frac{4\pi}{3}, \frac{3\pi}{2}
\]
Final Answer
The specific solutions to the equation \(\cos \theta + 2 \cos^2 \theta = 0\) in the interval \([0, 2\pi]\) are:
\[
\boxed{\left\{ \frac{\pi}{2}, \frac{2\pi}{3}, \frac{4\pi}{3}, \frac{3\pi}{2} \right\}}
\]