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GeoGebraGeoGebra Classroom

Rectangle Diagonals

Use coordinate geometry to prove that both diagonals of a rectangle are congruent. That is, write a coordinate geometry proof that formally proves what this applet informally illustrates. Be sure to assign appropriate variable coordinates to your rectangle's vertices! (The maximum number of variable coordinates your coordinate setup should have is 2.)
Now prove this same theorem true using the format of a 2-column proof or a paragraph proof. Hint: This proof may contain multiple pairs of congruent triangles.