Textbook Problem

In each of 7-14, the relation R is an equivalence relation on the set A. Find the distinct equivalence classes of R. $A=\left\{\left(1,3\right),\left(2,4\right),\left(-4,-8\right),\left(3,9\right),\left(1,5\right),\left(3,6\right)\right\}.$R is defined on A as follows: For every $\left(a,b\right),\left(c,d\right)\in A.$

$\left(a,b\right)R\left(c,d\right)\iff ab=bc.$