2

I have a question on the wording of the task

Find in $R^2$ the Hausdorff distance $h(S_7(a),(-9)S_1(b))$, where $a(2,-1)^T, b(-1,3)^T$

The first object is a circle with radius $7$ centered at point $a$, but in the second circle $-9$ what does it refer to? Do I need to multiply the radius of the circle by $-9$ or what operation should I do?

bubba
  • 43,483
  • 3
  • 61
  • 122
RoyalGoose
  • 135
  • 5
  • 2
    I'm not entirely sure, but it might mean that you multiply all the points in $S_1(b)$ by $-9$, coordinate-wise. – Michael Burr Jun 19 '21 at 21:15
  • You need to find the place in your class notes or textbook where this notation is defined. The definitions are not universal, so any answer you receive will just be a guess. – bubba Jun 19 '21 at 22:42

1 Answers1

1

It’s impossible to tell without the notation explicitly defined. However. A common use of the notation is as follows: If $X$ is a set, then $kX$ is the set $\{ k x : x \in X \}$.

So, in your problem, $-9 S_1(b) = \{ -9 x : x \text{ is a point of the unit circle centered at b} \}.$

RoyalGoose
  • 135
  • 5
NicNic8
  • 6,951