Chapter 2: Problem 11
Schreibe in der Form \(y=A \sin (\omega t+\alpha):\) (zeichnerische Lösung reicht aus) a) \(y=-2 \sin (5 t)+3 \cos (5 t)\) b) \(y=\sin (\pi t)-\cos (\pi t+\pi / 4)\)
Short Answer
Expert verified
a) \(y = \sqrt{13}\sin(5t - 0.588)\), b) \(y = \sqrt{2}\sin(πt - π/4)\)
Step by step solution
01
Rewrite the equation y = -2sin(5t) + 3cos(5t)
Firstly, recognize that the equation can be rewritten in phasor form if it matches the pattern \(A\sin(wt+α)\) by using the formula \(\sqrt{(-2)^2 + 3^2} = \sqrt{13}\) to solve for \(A\) and \(\arctan(-2/3) = -33.69^\circ\) will yield the phase offset \(α\). Convert the phase offset from degrees to radians => \(\alpha = -33.69^\circ \times \pi/180 = -0.588\) rad.
02
Check if the obtained solution are correct for equation y = -2sin(5t) + 3cos(5t)
Check by plugging in the values of \(A\), \(\omega\), and \(\alpha\) into \(A\sin(\omega t + \alpha)\). It should match the original equation. If it does, we've found our solution.
03
Rewrite the equation y = sin(πt) - cos(πt + π/4)
Similarly, for the equation use the formula \(\sqrt{1^2 + 1^2} = \sqrt{2}\) to solve for \(A\). Calculate phase offset using \(\arctan(-1/1) = -45^\circ\), and convert the phase offset from degrees to radians: \(\alpha = -45^\circ \times π/180 = -π/4\) rad.
04
Check if the obtained solution are correct for equation y = sin(πt) - cos(πt + π/4)
Check by plugging in the values of \(A\), \(\omega\), and \(\alpha\) into \(A\sin(\omega t + \alpha)\). It should match the original equation. If it does, then you've found your solution.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Sinusoidal Function Transformation
Sinusoidal function transformation is all about converting a trigonometric expression into a different form that is often easier to work with. In this exercise, we aim to express trigonometric equations in the form \(y = A \sin(\omega t + \alpha)\), which makes them more manageable to analyze or graph.
- Start by identifying the coefficients in front of the sine and cosine terms.
- The aim is to transform the original equation into a single sine equation with a specific amplitude, frequency, and phase shift.
- The combined effect of the sine and cosine components can be expressed as a single sine wave with a phase shift.
Phasor Representation
Phasor representation is a useful tool in analyzing trigonometric functions. Phasors can simplify the process of adding or subtracting sine and cosine waves.
- A phasor is a complex number that represents the magnitude and phase of a sinusoidal function.
- In the case of combining \(-2 \sin(5t) + 3 \cos(5t)\), the phasor provides a visual means to represent and combine these sinusoidal components.
- To find a phasor, calculate its magnitude \(A = \sqrt{(-2)^2 + 3^2} = \sqrt{13}\).
- The angle or phase is found using the arctangent function, \(\alpha = \arctan\left(-\frac{2}{3}\right)\).
Phase Angle Calculation
Calculating the phase angle is a critical part of transforming trigonometric functions into a single sinusoidal expression. The phase angle determines how much a wave is shifted horizontally compared to a standard sine or cosine wave.
- The phase angle \(\alpha\) is calculated using the arctangent function.
- This often involves determining the ratio of the sine and cosine coefficients, such as \(-\frac{2}{3}\) in the task.
- Use \(\arctan(-\frac{2}{3})\) to find the angle in degrees and then convert it to radians as needed: \(-33.69^\circ\) becomes \(-0.588\) radians.
- Ensure to adjust the angle to match the required quadrant for accurate representation.