Diameter of a Hyperbola

I. Introduction to Diameter:

  • In geometry, the diameter of a geometric figure is a line segment connecting two points on the curve and passing through the center. For a hyperbola, the concept of a diameter is specific and noteworthy.

II. Diameter of a Hyperbola:

  1. Definition:

    • The diameter of a hyperbola is a line segment passing through the center and having both endpoints on the hyperbola.
    • It is the longest chord of the hyperbola.
  2. Length:

    • The length of the diameter is twice the length of the semi-major axis.
    • For a hyperbola with the equation x2a2y2b2=1, the length of the diameter is 2a.

III. Properties and Characteristics:

  1. Symmetry:

    • The diameter is the axis of symmetry for a hyperbola. It divides the hyperbola into two symmetrical branches.
  2. Foci Relationship:

    • The foci of the hyperbola are located on the major axis, and the diameter passes through both foci.
    • The sum of the distances from any point on the hyperbola to the foci is constant and equal to the length of the major axis.


Consider the hyperbola given by the equation:


Let's find the diameter of this hyperbola.

1. Identify Key Parameters:

  • The given hyperbola is in the form x2a2y2b2=1.
  • In this case, a=4 (semi-major axis) and b=3 (semi-minor axis).

2. Calculate the Diameter:

  • The length of the diameter (D) is twice the length of the semi-major axis (a): D=2a

  • Substitute a=4 into the formula: D=2×4=8

3. Interpretation:

  • The diameter of the given hyperbola is 8.

4. Verification:

  • We can verify this by choosing two points on the hyperbola that lie on a line passing through the center and calculating the distance between them.

  • For instance, consider two points: A(4,3) and B(4,3). These points are symmetric with respect to the center at the origin.

  • The distance between these points using the distance formula: AB=(44)2+(33)2=64+36=100=10 As expected, AB is equal to the length of the diameter (D).