# binary relations help please :)

• Feb 13th 2010, 04:19 AM
Starlight87

consider a set S of all students, taking some courses chosen from a set of C courses: what are the binary relations?

R1= (S1,S2) : S1 and S2 take all the same courses together
R2=(S1,S2) : s1 and S2 take some courses together

are either equivalence relations too?

thanks a lot i would appreciate the help ^_^
• Feb 13th 2010, 05:15 AM
Plato
Quote:

Originally Posted by Starlight87
consider a set S of all students, taking some courses chosen from a set of C courses: what are the binary relations?
R1= (S1,S2) : S1 and S2 take all the same courses together
R2=(S1,S2) : s1 and S2 take some courses together

are either equivalence relations too?

Yes one of those is an equivalence relation.
• Feb 13th 2010, 08:08 AM
HallsofIvy
An equivalence relation must have three properties:

a) xRx for all x in the set. (reflexive property)
b) If xRy then yRx. (symmetric property)
c) If xRy and yRz then xRz. (transitive property).

You might want to take a close look at the transitive property for the relations you give.