Coordinate Proofs Math Example 1

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Example 1

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Use a coordinate proof to show that the diagonals of a rectangle are equal in length. Place the rectangle with one vertex at the origin.

Solution

  1. 1
    Step 1: Assign coordinates strategically. Place the rectangle with vertices at A(0,0)A(0,0), B(a,0)B(a,0), C(a,b)C(a,b), and D(0,b)D(0,b), where a,b>0a,b > 0.
  2. 2
    Step 2: Find the length of diagonal ACAC using the distance formula: AC=(aโˆ’0)2+(bโˆ’0)2=a2+b2AC = \sqrt{(a-0)^2 + (b-0)^2} = \sqrt{a^2+b^2}.
  3. 3
    Step 3: Find the length of diagonal BDBD: BD=(0โˆ’a)2+(bโˆ’0)2=a2+b2BD = \sqrt{(0-a)^2 + (b-0)^2} = \sqrt{a^2+b^2}.
  4. 4
    Step 4: Since AC=BD=a2+b2AC = BD = \sqrt{a^2+b^2}, the diagonals of the rectangle are equal in length. โ– \blacksquare

Answer

Both diagonals equal a2+b2\sqrt{a^2 + b^2}, so they are congruent.
Coordinate proofs work by assigning convenient variable coordinates to vertices, then computing distances, slopes, or midpoints algebraically. Placing one vertex at the origin and sides along the axes simplifies the arithmetic while keeping full generality.

About Coordinate Proofs

A method of proving geometric properties by placing figures on a coordinate plane and using algebraic formulas (distance, midpoint, slope) to verify relationships.

Learn more about Coordinate Proofs โ†’

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