2. 4 points Given two non-empty sets S1, S2 C R", define the operation S1 + S2 as follows: SitS2 := {zER" |z = xty for some x E S1, and for some y E S2} that is, the points z E S1 + S2 are those that can be expressed by the sum x + y for some x E S1, and y E S2. (a) 4 points Is it true that S1 + S2 must be convex for any nonempty convex sets S1 and S2? Justify your answer carefully