Use trigonometry in three dimensions
3D trigonometry is simply a twist of the ordinary trigonometric functions.
All you need are your 3 functions, sine, cosine and tangent, as well visualization skills, to figure it out.
The key to 3D trigonometry is to identify 2 or more linking triangles in the 3D figure.
How would you find the length of VA?
Because ABCD is a square base,
Using Pythagoras' theorem,
AD2 + CD2 = AC2 = 42 + 42 =32
AC = Sqrt 32
AO = (Sqrt 32) / 2
Using Pythagoras’ theorem,
AV2 = (Sqrt 32 / 2)2 + 32 = 32/4 + 32 = 17
AV = Sqrt 17