Problem: Prove that any element in the intersection of two sets is also in their union. I am reading a proof writing book for dummies & the solution given in text is: http://tinypic.com/r/141hn7/5 http://tinypic.com/r/141hn7/5 First Question: In exam/test, is it OK if I write the Statements only or do I need to write reasons as well (as shown in the pic). As, we are not suppose to write the proof in form of table but with every statement (which is already logically very clear in the pic) do I need to write the reason as well? Second Question: http://tinypic.com/r/et70jq/5 http://tinypic.com/r/et70jq/5 Similarly, if it is easy to draw figures then is it compulsory to add like this? PS. I will appreciate if your answers are in YES/NO form.