I don't know how to show the following are equivalence relations and if they are, how to describe equivalence classes.
1. a^2 + b^2=c^2 + d^2 where a,b,c,d are real numbers(describe equivalence cl)
2. For a pair of fractions a/b and c/d define a/b ~ c/d if ab=cd(same here)
1. (a,b)~(c,d) if a^2+b^2=c^2+d^2. ~ is an equivalent relation. We check the following.
(1) (a,b)~(a,b), obviously
(2) (a,b)~(c,d) ...
Equivalence Relations and Equivalence Classes are investigated.