Need Source of Projectile in Vacuum Outcome

https://www.physicsforums.com/showthread.php?t=75116 (the url has spaces) it said "shooting the projectile at 45 degrees will yield the greatest distance..." Where do you find that information. I need to know for my scientific experiment for school. I know this fact is true, but where is the source of this information? Thnx in advance.

Sorry if I post this is the wrong section. I really don't know where this thread should go

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Hootenanny
Staff Emeritus
$$s = v_0t+\frac{1}{2}at^2$$
$$v = \frac{d}{t} \Rightarrow t = \frac{d}{v}$$