$證明：?(1)?∵?A C ?平分? \angle DA B，$
$??C F \perp A B，??C E \perp A D?$
$∴?C E=C F，??\angle EA C=\angle BA C ?$
$在? Rt \triangle C D E ?和? Rt \triangle C B F ?中$
$? \begin{cases}{C E=C F}\\{C D=C B}\end{cases}?$
$∴?Rt \triangle C D E≌Rt \triangle C B F(\mathrm {HL})?$
$∴?\angle B=\angle C D E ?$
$∵?\angle C D E+\angle A D C=180°?$
$∴?\angle A D C+\angle B=180° ?$
$?(2)\ \mathrm {AF}=\frac {9}{2} ?$
