Questions tagged [reflection]
Reflection is a transformation that fixes a line or plane or a more general subset. Reflections appear in geometry, linear algebra, complex analysis, differential equations, etc -- therefore, this tag must be used with a tag describing the area of mathematics.
604 questions
3 votes
1 answer
56 views
Reflecting a point $(x,y)$ about a line $y=mx+b$
If given a point $(x,y)$, and told to reflect it across a given line $y=mx+b$, there are several ways that this can be achieved. For one, the most simple way is to just count the diagonals, but this ...
1 vote
1 answer
78 views
Wythoffian constructions and polyhedra expansion
I'm trying to understand to Wythoffian constructions. In particular, how to show that when additional mirror is activated, all the previous faces remain (translated and dilated) and are separated by ...
2 votes
2 answers
82 views
Isotopy of $\mathbb{R}^{2}$ that *swaps* two functions (or a function and its reflection)
From a previous post, the following fact has been brought to my attention: For any two continuous functions $f, g: \mathbb{R} \rightarrow \mathbb{R}$, the following function is an isotopy of $\mathbb{...
2 votes
2 answers
134 views
Minimum Perimeter of triangle with co-ordinate axes as two sides and the third side passing through the point $(8,1)$
A straight line with a negative slope passes through the point $P(8,1)$ and meets x-axis at $A$ and the y-axis at $B$. Find the minimum possible value of the perimeter of $\triangle AOB$. My Attempt ...
0 votes
1 answer
42 views
Ambient Isotopy of $\mathbb{R}^{2}$ Taking a Function to Its Reflection About the $x$-Axis
Let $A$ be a subset of $\mathbb{R}$ and let $f: A \rightarrow \mathbb{R}$ be a continuous function. If $f(x) = mx$ for some positive number $m > 0$, then the function $H: \mathbb{R}^{2} \times [0, ...
0 votes
1 answer
33 views
Deriving the inequality $|R(1,w)|\geq k$ via wall-crossing parity in Davis's Coxeter Groups book
Suppose $\mathbf{s}=(s_1,\dots,s_k)$ is a word in $S$. Define $w_i\in W$ by $w_0=1$ and $w_i=s_1\cdots s_i$, and $r_i\in R$ by $r_i=w_{i-1}s_iw_{i-1}^{-1}$. Set $\Phi(\mathbf{s}):=(r_1,\dots,r_k)$. ...
0 votes
0 answers
31 views
Exceptional complex reflection groups acting irreducibly on the adjoint representation
$\DeclareMathOperator\PSU{PSU}\DeclareMathOperator\U{U}\DeclareMathOperator\SU{SU}\DeclareMathOperator\O{O}\DeclareMathOperator\SO{SO}\DeclareMathOperator\GL{GL}\DeclareMathOperator\ASL{ASL}\...
2 votes
1 answer
158 views
algebra error occurs when I generalize a reflection formula
I was able to find the following formula when reflecting a point $(x,y)$ to point $(x^\prime,y^\prime)$ over the line $y = mx$: $$(x^\prime,y^\prime)=\left(\frac{1-m^2}{1+m^2}x+\frac{2m}{1+m^2}y,\frac{...
1 vote
0 answers
39 views
Number of reflections between two hyperbolic mirrors
Let two mirror surfaces be defined by the graphs of functions $y=\frac{1}{x}$ and $y=-\frac{1}{x}$ for all $x>0$. A beam of light originates at the point $(0, a)$ $(a>0)$ and travels ...
0 votes
1 answer
58 views
standard mapping notation for rotations and reflections
Is there a standard mapping notation for rotations and reflections? Some sources I've looked at use R for rotations and r for reflections, others don't really make a distinction and may use the same ...
3 votes
1 answer
185 views
Decompose a set into reflectional symmetric sets
Suppose I have a finite set $S$ in $\mathbb{R}^n$ and reflections $\sigma_j$ defines as follow:$$\sigma_ j x=\sigma_j(x_1,\ldots,x_{n})=(x_1,\ldots,-x_j,\ldots,x_{n})$$ Formerly, I tried to decompose $...
0 votes
1 answer
58 views
looking for general rotation and reflection formulas for cartesian coordinate systems
Translations are easy in Cartesian coordinates since each point P can be moved to its corresponding point P$^\prime$ with either a 2-component vector on the plane or a 3-component vector in space. ...
0 votes
1 answer
289 views
Reflection of light to certain point using mirrors
As shown in the diagram, a laser light originates vertically from point $A$ and must reach point $T$. There are two rotating mirrors that adjust their angles based on a given relationship with $\theta$...
0 votes
1 answer
44 views
A problem on conjugations in Weyl groups.
To the best of my knowledge, if $R$ is a (reduced) irreducible root system in some real vector space $V$, then its Weyl group $W(R)$ is the finite Coxeter group generated by the reflections associated ...
2 votes
0 answers
121 views
Question about Reflecting Barriers
I am reading "Reflecting Barriers" related chapters in Cox and Miller's book "The theory of stochastic processes". On page 224 it says that: $"$ Consider a Wiener process $X(t)$ ...