Find the angle.?

With respect to ∠X, XY is the adjacent side, YZ is the opposite side, and ZX is the hypotenuse.

tan∠X = (opposite side) / (adjacent side)
tan∠X = YZ/XY
Hence, tan∠X = 21/20

21/20 = 1.05 = tan of angle x

(The angle is 46.4 deg)

Start with the Greeks and just go from there.

https://www.youtube.com/results?search_query=ancient+greek+mathematics

Did you know that every single stone in the make up of the Parthenon is unique none of them are the same size or shape?
http://www.mathematicsmagazine.com/Articles/Mathematics_ofTheParthenon.php#.WIeLZFWLSwU

tan x = opp/adj= 21/20
https://gyazo.com/ee4c855074f49566061d71311dfdad5f

In right triangle XYZ XY is 20, YZ is 21 and ZX is 29. Find the tangent of angle X.
For angle X
Adjacent side =XY=20
Facing side=YZ=21
Hence tan X = Facing side / Adjacent side =21/20=1.05
Angle X= tan⁻1(1.05)=46.40°

Tan(angle) = opposite / adjacent
Tan(angle) = YZ/XY = 21/20
Tan(aangle) = 1 1/20 = 1.05
Angle = Tan^-1(1.05)
Angle = 46.39 degrees (2 d.p.).

S