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Several difficult problems of mathematical geometry in senior two (advanced! ! )
1, b is BF parallel to CD, and d is DF⊥CD.

A is AG⊥BF in g and AH⊥DF in H.

∴∠FBA=30,∠DBF=45

∴BG=6, BF=DF=5 times the root number 2.

FH=AG=2 times the root number 3,

∴AH=FG=(5 times the root number 2)-6

DH = (5th root number 2)-(2nd root number 3)

∴ ad = (the square of DH+the square of ah) under the root sign.

CD= 10 times the root number 2.

(Ignore unit)