解: ∵$\angle A C B=90°,$$ \angle B+\angle A+\angle A C B=180° ($已知)
∴$\angle B+\angle A=180°-\angle A C B=90° ($等式性质)
∵$\angle B=\angle E ($已知)
∴$\angle E+\angle A=90° ($等量代换)
∵$\angle A+\angle E+\angle A D E=180° ($已知)
∴$\angle A D E=180°-\angle E-\angle A=90° ($等式性质)