As shown in the figure, in the linear triangle ABC, ∠ C = 90 °, BD is the angular bisector of △ ABC, be is the angular bisector of △ BDA, DF is the height of △ BDE

In △ BDF, ∠ FDB can be known, so ∠ DBF can be obtained;
∠DBF=∠EBA=1/2∠CBD;
So we can find ∠ a
Very basic Dongdong, spend time, online is useful

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