Turning 21" Monitors 90 Degrees

So at the moment I have two 21" monitors running off my computer, but in the future I plan on purchasing a 27" 2560x1440p monitor. When I get the 27" monitor I want to be able to mount and turn the 21" monitors on each side of the 27" monitor. Do you guys have any idea as to how to do this? I have a slight idea of how to do so but I would love to hear what you guys have to say! Thanks it's greatly appreciated!

Well first do the 21" monitors have VESA mounts?  Or do they have nothing (like mine :(...)?

Both of them do

Then look for a 3 way VESA mount.  There should be one with adjustable arms so you can configure the monitors in the form you need.  Just google and im sure youl find something!  If  nothing else you could get a 2 arm bracket for the 21" monitors and just sit the 27" inbetween.

More to the point lets do the math 

First lets do a typical 16x9 right angle tri-angle using the Pythagoras theorem it tells us that angle a is about 29.4 degrees.

So now we take that  and run it again on a 21 inch diagonal and get about 18.3 inch on the bottom which is what I think you want to be your new side, right?

now if we run the formula with a 27 inch panel we get a height of about 13.3 inches so you will have about 5 inches over hang by doing this it evens out around 39 ish inch pannel.

that is today's lesson in math, I say about and around due to different bezel sizes. 

PS this is handy