Proof: make a quadrilateral ABCD

∵∠ A+∠ B+∠ C+∠ D = 360 (the sum of the internal angles of the quadrilateral is equal to 360).

Or ≈A =∠B =∠C =∠d?

∴ 4 ∠ A = 360 (equivalent replacement)

∴∠A=90

Similarly, ∠B=∠C=∠D=90 degrees.

∴ Quadrilateral ABCD is a rectangle (the nature of a rectangle)

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