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 Cole Garza. in the United States
Jan 24,2025

Real Tutor Solution

Tutor-Verified Answer

Answer

The solutions are \( x = \arctan\left(\frac{12}{5}\right) + k\pi \) for all integers \( k \).

Solution

To solve the equation \( 5\sin(x) - 12\cos(x) = 0 \) using the auxiliary angle method, follow these steps: ### **1. Express the Equation in the Form \( R\sin(x + \alpha) = 0 \)** The general form for such an expression is: \[ a\sin(x) + b\cos(x) = R\sin(x + \alpha) \] where: \[ R = \sqrt{a^2 + b^2} \] \[ \alpha = \arctan\left(\frac{b}{a}\right) \] For the given equation: \[ a = 5 \quad \text{and} \quad b = -12 \] Thus, \[ R = \sqrt{5^2 + (-12)^2} = \sqrt{25 + 144} = \sqrt{169} = 13 \] \[ \alpha = \arctan\left(\frac{-12}{5}\right) = -\arctan\left(\frac{12}{5}\right) \] ### **2. Rewrite the Original Equation** \[ 5\sin(x) - 12\cos(x) = 13\sin\left(x - \arctan\left(\frac{12}{5}\right)\right) = 0 \] ### **3. Solve for \( x \)** Set the sine function to zero: \[ 13\sin\left(x - \arctan\left(\frac{12}{5}\right)\right) = 0 \implies \sin\left(x - \arctan\left(\frac{12}{5}\right)\right) = 0 \] \[ x - \arctan\left(\frac{12}{5}\right) = k\pi \quad \text{for integer } k \] \[ \Rightarrow x = \arctan\left(\frac{12}{5}\right) + k\pi \] ### **4. Find All Solutions Within One Period (\( 0 \leq x < 2\pi \))** The principal solutions within one period are: \[ x = \arctan\left(\frac{12}{5}\right) \quad \text{and} \quad x = \arctan\left(\frac{12}{5}\right) + \pi \] ### **Final Answer** All real numbers congruent to arctan (12⁄5) modulo π. In other words, the solutions are x = arctan(12/5) + k π for all integers k.

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The Deep Dive

To solve the equation \( 5\sin(x) - 12\cos(x) = 0 \) using the auxiliary angle method, we can rewrite it in the form \( R\sin(x + \phi) = 0 \) where \( R = \sqrt{a^2 + b^2} \) and \( \tan(\phi) = \frac{b}{a} \). In our case, \( a = 5 \) and \( b = -12 \). First, we calculate \( R \): \[ R = \sqrt{5^2 + (-12)^2} = \sqrt{25 + 144} = \sqrt{169} = 13. \] Next, we find \( \phi \): \[ \tan(\phi) = \frac{-12}{5}. \] This angle \( \phi \) is in the fourth quadrant since the sine component is positive and the cosine component is negative. Thus, we have: \[ \phi = \tan^{-1}\left(-\frac{12}{5}\right). \] To find \( x \), we can rewrite the equation: \[ 5\sin(x) = 12\cos(x) \implies \tan(x) = \frac{12}{5}. \] Now, we solve for \( x \): \[ x = \tan^{-1}\left(\frac{12}{5}\right). \] This gives us one solution for \( x \). Since the tangent function has a period of \( \pi \), the general solutions are: \[ x = \tan^{-1}\left(\frac{12}{5}\right) + n\pi, \quad n \in \mathbb{Z}. \] Within one period, \( [0, 2\pi) \), we find the specific values: 1. \( x_1 = \tan^{-1}\left(\frac{12}{5}\right) \) 2. \( x_2 = x_1 + \pi \) Thus, all possible values of \( x \) within one period are \( \tan^{-1}\left(\frac{12}{5}\right) \) and \( \tan^{-1}\left(\frac{12}{5}\right) + \pi \).

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