**Solution:**

(a) We have (opp. angles of parallelogram)

(opp. sides of parallelogram)

(opp. sides of parallelogram)

Thus, (SAS)

Similarly, (SAS)

(SAS)

Thus,

(proved)

(b)

(vert. opp. angles)

(alt. angles)

(alt. angles)

Thus, is similar to (AAA)

Hence,

Thus,

(proved)