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Ch. 5 - Complex Numbers, Polar Coordinates and Parametric Equations
Blitzer - Trigonometry 3rd Edition
Blitzer3rd EditionTrigonometryISBN: 9780137316601당신이 사용하는 게 아니라요?교과서 변경
5장, 문제 31

In Exercises 27–32, select the representations that do not change the location of the given point. (−5, − π/4) (−5, 7π/4)

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1
Understand that the point is given in polar coordinates as \((r, \theta)\), where \(r\) is the radius (distance from the origin) and \(\theta\) is the angle measured from the positive x-axis.
Recall that changing the angle \(\theta\) by adding or subtracting full rotations of \(2\pi\) radians (i.e., \(\theta + 2k\pi\), where \(k\) is an integer) does not change the location of the point because angles are periodic with period \(2\pi\).
Note that changing the radius \(r\) to its negative value \(-r\) and adding \(\pi\) to the angle \(\theta\) (i.e., \((-r, \theta + \pi)\)) also represents the same point, because moving in the opposite direction by \(\pi\) radians with a negative radius points to the same location.
Apply these principles to the given points: for \(( -5, -\frac{\pi}{4} )\), consider if changing the angle by \(2\pi\) or adding \(\pi\) to the angle and negating the radius results in the same point; similarly, analyze \(( -5, \frac{7\pi}{4} )\) under these transformations.
Summarize which representations keep the point's location unchanged by verifying if the transformed coordinates correspond to the same position in the plane using the above rules.

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이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.
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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Polar Coordinates and Their Representation

Polar coordinates represent points in the plane using a radius and an angle, written as (r, θ). The radius r is the distance from the origin, and θ is the angle measured from the positive x-axis. Understanding how points are plotted in polar form is essential to analyze transformations that affect their location.
추천 영상:
05:32
Intro to Polar Coordinates

Equivalent Polar Coordinates

A single point in polar coordinates can have multiple representations due to periodicity of angles and sign changes in radius. For example, (r, θ) is equivalent to (−r, θ + π) and (r, θ + 2πk) for any integer k. Recognizing these equivalences helps identify which transformations preserve the point's location.
추천 영상:
05:32
Intro to Polar Coordinates

Effect of Angle and Radius Transformations on Point Location

Changing the angle by adding multiples of 2π or adjusting the radius sign with a corresponding angle shift can produce the same point. However, other transformations may move the point. Understanding how these changes affect the point's position is key to selecting representations that do not alter its location.
추천 영상:
4:25
Graphs of Shifted and Reflected Functions