解：?$(1) \frac {OC}{OD}=\frac {20}{24}=\frac 56，$??$\frac {OA}{OB}=\frac 56$?
∴?$\frac {OC}{OD}=\frac {OA}{OB}，$??$∠AOB=∠COD$?
∴?$△AOB∽△COD$?
?$(2) \frac {ED}{DF}=\frac {30}{48}=\frac 58，$??$\frac {AB}{AC}=\frac {45}{72}=\frac 58$?
∴?$\frac {ED}{DF}=\frac {AB}{AC}$?
又?$∠A=∠D$?
∴?$△EDF∽△BAC$?
