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8 lines
415 B
8 lines
415 B
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- $\triangle ABF \cong \triangle AED$
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- $\therefore \angle 2=\angle BAF$
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- $\because \angle 3+\angle FAB=90^{\circ}$
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- $\therefore \angle 2+\angle 3=90^{\circ}$
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- 画出外接隐藏圆，以$O$为圆心
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- 套路，满满的套路！找出一个三角形吧：$\triangle OGB$!,$BG>=OB-OG$! |