I'm stuck on some proofs, wondering if anyone could lend a hand.

Let S be a subset ofR

a) Prove: bd (S) = (cl S) ∩ [cl (R\S)]

b) Prove: bd (S) is a closed set

*bd (S) is a boundary point of S. cl (S) is a closure of S. (R\S) is S^c (compliment of S)*