How can you find a reflection matrix about a given

Celia Horne

Celia Horne

Answered question

2022-01-31

Find a reflection matrix about a given line, using matrix multiplication and the idea of composition of transformations.
The line of: y=2x3, all in R2

Answer & Explanation

dikgetse3u

dikgetse3u

Beginner2022-02-01Added 10 answers

So you have a vector (x1,y1)T, and you need to locate a matrix M that is such that (x2,y2)T=M(x1,y1)T is the reflection across y=2x3
So what does the reflection means? It means that the middle of the two points is on the line of reflection, and the line between those points is perpendicular to the reflection line. The first condition can be written as 
y1+y22=23x1+x22 
The second condition means that the slope of the line between the two points is 1m where m is the slope of the reflection line: 
y2y1x2x1=123=32  
Now you type x2 and y2 in terms of x1 and y1
x2=m11x1+m12y1 
y2=m21x1+m22y1 
Next, the matrix you are looking for has these coefficients. 
M=(m11m12m21m22)

Karly Logan

Karly Logan

Beginner2022-02-02Added 11 answers

Rotating the plane to make the line appear straighter is one tactic. y=0, apply the reflection in the x-axis, and then rotate back. 
First tanθ=23. Then the required matrix is 
(cosθsinθsinθcosθ)(1001)(cosθsinθsinθcosθ) 
=(cos2θsin2θsin2θcos2θ)

Do you have a similar question?

Recalculate according to your conditions!

New Questions in Linear algebra

Ask your question.
Get an expert answer.

Let our experts help you. Answer in as fast as 15 minutes.

Didn't find what you were looking for?