The following are equivalent in boolean algebra.
1) a+b=b

2) a*b=a

3) a'+b=1

4) a*b'=0

a)Proove the equivalence of (1) and (2).
b)Proove the equivalence of (1) and (3).

a) $a \subseteq b$ you figure out why from (1) and apply it to show (2)