How can I determine if a set is convex without graphing it?
I have that a set, , is convex if, given any two points, , the line connecting them is entirely within , or:
Some of the sets in question:
I have to hand in f. I'm not good enough to draw it, but I can envision it. It looks like a "V" going from down to . Clearly, it is not convex. But how would I show that mathematically?