You can put this solution on YOUR website! ABCD is a square. Prove that AC = BD
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We are given that ABCD is a square. AD=BC by the properties of a square.
Angle BAD = Angle ABC by the properties of a square, and each are 90 degrees.
AB = BA by the Reflexive property.
Triangle ABD ≅ Triangle BCA by the SAS postulate.
AC=BD by CPCTC.
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Hope I helped!