Question

Given the equation \( 5\sin(x) - 12\cos(x) = 0 \), use the auxiliary angle method to find all possible values of x within one period.

Ask by Love Mullins. in the United States
Jan 21,2025

Real Tutor Solution

Tutor-Verified Answer

Answer

The solutions within one period are: \[ x = \arctan\left(\frac{12}{5}\right) \quad \text{and} \quad x = \pi + \arctan\left(\frac{12}{5}\right) \]

Solution

To solve the equation \( 5\sin(x) - 12\cos(x) = 0 \) using the **auxiliary angle method**, follow these steps: 1. **Express in the Form \( R\sin(x + \alpha) \):** The expression \( 5\sin(x) - 12\cos(x) \) can be rewritten using the auxiliary angle formula: \[ a\sin(x) + b\cos(x) = R\sin(x + \alpha) \] where: \[ R = \sqrt{a^2 + b^2} \] \[ \tan(\alpha) = \frac{b}{a} \] For the given equation: \[ a = 5, \quad b = -12 \] \[ R = \sqrt{5^2 + (-12)^2} = \sqrt{25 + 144} = \sqrt{169} = 13 \] \[ \tan(\alpha) = \frac{-12}{5} \implies \alpha = \arctan\left(-\frac{12}{5}\right) = -\arctan\left(\frac{12}{5}\right) \] Thus, the equation becomes: \[ 13\sin(x - \arctan(12/5)) = 0 \] Simplifying: \[ \sin\left(x - \arctan\left(\frac{12}{5}\right)\right) = 0 \] 2. **Solve for \( x \):** The sine function equals zero at integer multiples of \( \pi \): \[ x - \arctan\left(\frac{12}{5}\right) = n\pi \quad \text{where } n \text{ is an integer} \] Solving for \( x \): \[ x = n\pi + \arctan\left(\frac{12}{5}\right) \] Within one period (\( 0 \leq x < 2\pi \)), there are two solutions corresponding to \( n = 0 \) and \( n = 1 \): \[ x_1 = \arctan\left(\frac{12}{5}\right) \] \[ x_2 = \pi + \arctan\left(\frac{12}{5}\right) \] 3. **Final Answer:** All solutions within one period are: \[ x = \arctan\left(\frac{12}{5}\right) \quad \text{and} \quad x = \pi + \arctan\left(\frac{12}{5}\right) \] **Summary:** The solutions to \( 5\sin(x) - 12\cos(x) = 0 \) within one period \( [0, 2\pi) \) are: \[ x = \arctan\left(\frac{12}{5}\right) \quad \text{and} \quad x = \pi + \arctan\left(\frac{12}{5}\right) \] Answer: All real numbers congruent to arctan 12⁄5 or to π plus arctan 12⁄5. Thus, within one period, x = arctan(12/5) and x = π + arctan(12/5)

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Beyond the Answer

To solve the equation \( 5\sin(x) - 12\cos(x) = 0 \) using the auxiliary angle method, we can rewrite it in the form \( R\sin(x + \phi) = 0 \). First, we need to express the equation in terms of sine and cosine. We rearrange it to: \[ 5\sin(x) = 12\cos(x) \] Dividing both sides by \( \cos(x) \) (assuming \( \cos(x) \neq 0 \)), we get: \[ \tan(x) = \frac{12}{5} \] Using the auxiliary angle, we write the equation as: \[ R\sin(x + \phi) = 0 \] where \( R = \sqrt{5^2 + 12^2} = \sqrt{25 + 144} = \sqrt{169} = 13 \). Next, we find the angle \( \phi \) such that: \[ \cos(\phi) = \frac{12}{13}, \quad \sin(\phi) = \frac{5}{13} \] Thus, \( \phi = \tan^{-1}\left(\frac{5}{12}\right) \). Now we set up the equation: \[ \sin(x + \phi) = 0 \] This gives us: \[ x + \phi = n\pi \quad (n \in \mathbb{Z}) \] Solving for \( x \): \[ x = n\pi - \phi \] Since we want values of \( x \) within one period (i.e., \( [0, 2\pi) \)), we consider \( n = 0 \) and \( n = 1 \): 1. For \( n = 0 \): \[ x = -\phi \quad \text{(not in } [0, 2\pi) \text{, so we discard)} \] 2. For \( n = 1 \): \[ x = \pi - \phi \] 3. For \( n = 2 \): \[ x = 2\pi - \phi \] Now, substituting \( \phi \): 1. \( x_1 = \pi - \tan^{-1}\left(\frac{5}{12}\right) \) 2. \( x_2 = 2\pi - \tan^{-1}\left(\frac{5}{12}\right) \) To evaluate numerically (using \( \tan^{-1}\left(\frac{5}{12}\right) \approx 0.39479 \) radians): 1. \( x_1 \approx \pi - 0.39479 \approx 2.74680 \) 2. \( x_2 \approx 2\pi - 0.39479 \approx 5.88834 \) Thus, the possible values of \( x \) within one period \( [0, 2\pi) \) are: \[ x \approx 2.74680 \quad \text{and} \quad x \approx 5.88834 \]

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