Prove that the diagonals of a rectangle are of equal length

Prove that the diagonals of a rectangle are of equal length.

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ABCD is a rectangle with AC and BD as its diagonals.
ABCD is a rectangle
∴∠A = 90o, AD = BC
AD//BC and AB is a transversal
∴∠A +∠B = 180o
⇒ ∠B = 90o
In ∆ ABD and ∆ BAC
AB = BA
∠A = ∠B
AD = BC
∴∆ABDimage ∆BAC
⇒ BD = AC (c.p.c.t)
Hence, the diagonals of a rectangle are equal.