Let df=x and r be the radius of the circumscribed sphere. So af=ef=√ x? +4. Because ec+4=2r in trapezoidal abce, ec=2r-4. Where r= 1/2ae.

Simultaneous, r=(8-x-√4+x? )/2=(√(4+(√x？ +4

+

x)？ ) /2, the solution is x =161120, that is, df =161/20. Bring it in, find R, and then find ag. And (ag-df)? +4=fg？ , you can find fg. Hope to adopt.