I have this question:
Probability distributions (joint)-screen-shot-2013-03-11-11.40.06.png
and I'm a little confused. To calculate joint distributions in the earlier questions i was using:

P_{(\xi1,\xi2)}(x1,x2)=P_{(\xi1)}(x1)P_{(\xi2)}(x2  )

But that would mean that if:

P_{(\xi1,\xi2)}(2,0)=0\  either\  P_{(\xi1)}(2)=0\  or\  P_{(\xi2)}(0)=0

which cant be true in either case as

P_{(\xi1,\xi2)}(1,0)\  isnt\  0\  and\ neither\ is\ P_{(\xi1,\xi2)}(2,1)

Can someone please explain what I'm missing. Thanks :/