Chapter 2: Q15 (page 42)
Consider the following statements:
Reflexive Property: Robot A is as rusty as itself.
Symmetric Property: If Robot A is as rusty as Robot B, then Robot B is as rusty as Robot A.
Transitive Property: If Robot A is as rusty as Robot B and Robot B is as rusty as Robot C, then Robot A is as rusty as Robot C.
A relation such as 鈥渋s as rusty as鈥 that is reflexive, symmetric, and transitive is an equivalence relation. Which of the following are equivalence relations?
a. Is rustier than
b. Has the same length as
c. Is opposite (for rays)
d. Is coplanar with (for lines)

Short Answer
鈥楬as the same length as鈥 is an equivalence relation.

