Analytic Geometry Math Example 2

Follow the full solution, then compare it with the other examples linked below.

Example 2

hard
Use coordinates to prove that the diagonals of a rectangle bisect each other.

Solution

  1. 1
    Place the rectangle with vertices at A(0,0)A(0,0), B(a,0)B(a,0), C(a,b)C(a,b), D(0,b)D(0,b) where a,b>0a,b>0.
  2. 2
    Find the midpoint of diagonal ACAC: M1=(0+a2,0+b2)=(a2,b2)M_1 = \left(\frac{0+a}{2}, \frac{0+b}{2}\right) = \left(\frac{a}{2}, \frac{b}{2}\right).
  3. 3
    Find the midpoint of diagonal BDBD: M2=(a+02,0+b2)=(a2,b2)M_2 = \left(\frac{a+0}{2}, \frac{0+b}{2}\right) = \left(\frac{a}{2}, \frac{b}{2}\right).
  4. 4
    Since M1=M2M_1 = M_2, the diagonals share the same midpoint, so they bisect each other.

Answer

Both diagonals have midpoint (a2,b2)\left(\dfrac{a}{2}, \dfrac{b}{2}\right), so they bisect each other.
Placing a figure in a coordinate system with strategic vertices at the origin and on the axes simplifies midpoint calculations. When two segments share a midpoint, they bisect each other, a key analytic geometry proof technique.

About Analytic Geometry

Analytic geometry studies geometric objects using coordinate systems and algebraic equations, translating shapes into formulas so that algebra can solve geometry problems. This field, founded by Descartes, unifies algebra and geometry.

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