Solving Reflection Matrix Homework: Angle & Rotation About Origin

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Homework Help Overview

The discussion revolves around determining the nature of a given matrix, specifically whether it represents a rotation about the origin or a reflection about the positive x-axis. The matrix in question is provided, and participants are exploring the implications of its determinant and the angle associated with it.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are examining the determinant of the matrix to infer its properties, with one noting that a determinant of -1 suggests reflection. There are inquiries about how to find the angle that the line makes with the x-axis, and attempts to project onto the axis have been mentioned. Some participants are questioning whether the matrix could represent both a rotation and a reflection.

Discussion Status

The discussion is active, with participants providing insights and clarifications regarding the relationship between the matrix properties and geometric transformations. There is a mix of interpretations about the matrix's nature, and some guidance has been offered regarding the forms of rotation and reflection matrices, though no consensus has been reached.

Contextual Notes

Participants are working within the constraints of the homework problem, which does not provide additional context or information about the matrix's application. There is an emphasis on understanding the definitions and implications of the matrix's determinant and its geometric interpretations.

Lchan1
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Homework Statement


Given the matrix A=
-1/2 root(3)/2
root(3)/2 1/2

determine if the matrix is a rotation about the origin or a reflection about the positive x axis
and find the angle between the that the line makes with the x-axis



Homework Equations





The Attempt at a Solution



I found the det(A)=-1 can I concluded that the matrix reflects vectors?
and also how do you find the angle?
I tried doing projection onto the axis. but didnt get me anywhere
please help..
 
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Hi Lchan1! :smile:

(have a square-root: √ :wink:)
Lchan1 said:
I found the det(A)=-1 can I concluded that the matrix reflects vectors?

Yup! :smile:
and also how do you find the angle?

learn this:

rotation through angle θ is

cosθ sinθ
-sinθ cosθ :wink:
 
does that mean it's a rotation and a reflection?
pi/3 will be the angle?
 
Lchan1 said:
does that mean it's a rotation and a reflection?
pi/3 will be the angle?

sorry, I was a bit too cryptic last time :redface:

a combination of a rotation and a reflection is a reflection …

it would have been better if I'd said

rotation through angle θ is

cosθ sinθ
-sinθ cosθ

reflection about y-axis is

-1 0
0 1

and if you combine them you get … ? :smile:
 

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