In: Math
Please Consider the function f : R -> R given by f(x, y) = (2 - y, 2 - x).
(a) Prove that f is an isometry.
(b) Draw the triangle with vertices A = (1, 2), B = (3, 1), C = (3, 2), and the triangle with vertices f(A), f(B), f(C).
(c) Is f a rotation, a translation, or a glide reflection? Explain your answer.
(a) Lets prove that the function f preserve the distance. For this. let us assume any two points P (x1, y1) and another point Q (x2, y2), then
Using the definition of isometry f : R --> R, we have
Now, using the distance formula for points P' and Q', we have
Therefore, f is an isometry.
(b) The triangle ABC, with vertices A = (1, 2), B = (3, 1), C = (3, 2), and the triangle A'B'C' with vertices f(A)=A', f(B)=B', and f(C)=C' are shown in figure below:
(c) We see from the figure that the triangle ABC is the reflection about the line x + y = 2. So, the triangle A'B'C' can be obtained by roatating clockwise direction (270o - 2 tan-1(-1/2)) about point (-1, 3). So, it requies both translation and rotation. So, we can put it under a glide reflection