边角

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∵AB=AC∴∠ABC=∠ACB=45°∴∠BAC=90(三角形内角和180°)∵AF是∠BAC的角平分线∴∠BAF=∠CAF=45°∴∠BAF=∠ACB∵∠BAC=90°∴∠ABD+∠ADB=90°