I am assuming you have the Optiplex 3020. This page at hardware-corner states that it is compatible and this forum post would also seem to confirm it. However this forum post has more information and the form factor of your system comes into play as well due to the wattage of the PSU.
and i wanna also know what is the max gpu can i use it in this motherboard 040ddp a1
Can Dell 040DDP A01  support  i7-4790 ?