(8 pts) a) (4 pts)Suppose R is the relation on N where aRb means that a starts in the same digit in which b starts. Determine whether Ris an equivalence relation on N. Justify your answer. b) (4 pts) Suppose the relation Ris defined on the set Z where aRb means that ab < 0. Determine whether R is an equivalence relation on Z. Justify your answer.