Look at the orthohedron in the figure.CG=12HG CG=\frac{1}{2}HG CG=21HGCalculate BE BE BE.
5+X5+X5+XAAABBBCCCDDDEEEFFFGGGHHH
x52+552 x\frac{\sqrt{5}}{2}+\frac{5\sqrt{5}}{2} x25+255