∫ rt △ the coordinate of OAB vertex A is (9,0),
∴OA=9,
∫tan∠BOA = 33,
∴AB=33,∠B=60,
∴∠AOB=30,
∴OB=2AB=63,
According to the triangle area formula, s △ OAB =12× OA× ab =12× ob× am, that is, 9×33=63AM.
∴AM=92,
∴AD=2×92=9,
∠∠AMB = 90,∠B=60,
∴∠BAM=30,
∫∠BAO = 90,
∴∠OAM=60,
∵DN⊥OA,
∴∠NDA=30,
∴AN= 12AD=92, which is obtained by Pythagorean theorem: DN=AD2? AN2