20 18 Liaoyang as shown in the figure, centered at 0 o'clock at the corner mon.

Because ag = AE ∠ GAF = ∠ EAF =15; AF=AF, so △GAF is all equal to △ △EAF.

So GF=EF

At the same time, ∠ FGC = ∠ AFE = ∠ CFD = 60 can be obtained.

Therefore, since gf = dfCF = CF∠ GCF =∠ DCF = 45, △CGF is equal to △CDF.

So gf = df

Comprehensive available ef = df