from geometry point:
let DP perpendicular to AB, where P lies on AB. Since triangle ABC is iso-right triangle, so DP=1/2 AB = 1/ AD (as AB=AD)
Therefore, for right-triangle ADP, <DAP=30. should be easy going forward.
let DP perpendicular to AB, where P lies on AB. Since triangle ABC is iso-right triangle, so DP=1/2 AB = 1/ AD (as AB=AD)
Therefore, for right-triangle ADP, <DAP=30. should be easy going forward.
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