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Conic Sections - Standard equation of Hyperbola

Grade 11CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A hyperbola is the set of all points in a plane, the difference of whose distances from two fixed points (foci) in the plane is a constant. This constant is denoted by 2a2a.

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The line through the foci is called the transverse axis, and the line through the center and perpendicular to the transverse axis is called the conjugate axis.

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The distance between the two foci is 2c2c, the distance between the two vertices is 2a2a, and the length of the conjugate axis is 2b2b. These are related by the equation c2=a2+b2c^2 = a^2 + b^2.

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The eccentricity ee of a hyperbola is the ratio of the distance from the center to a focus to the distance from the center to a vertex, given by e=cae = \frac{c}{a}. For every hyperbola, e>1e > 1.

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The latus rectum of a hyperbola is a line segment perpendicular to the transverse axis through any of the foci, with its endpoints lying on the hyperbola.

📐Formulae

x2a2−y2b2=1 (Transverse axis along x-axis)\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1 \text{ (Transverse axis along x-axis)}

y2a2−x2b2=1 (Transverse axis along y-axis)\frac{y^2}{a^2} - \frac{x^2}{b^2} = 1 \text{ (Transverse axis along y-axis)}

c2=a2+b2c^2 = a^2 + b^2

e=ca=a2+b2ae = \frac{c}{a} = \frac{\sqrt{a^2 + b^2}}{a}

Length of Latus Rectum=2b2a\text{Length of Latus Rectum} = \frac{2b^2}{a}

Foci (horizontal):(±c,0), Vertices (horizontal):(±a,0)\text{Foci (horizontal)}: (\pm c, 0) \text{, Vertices (horizontal)}: (\pm a, 0)

Foci (vertical):(0,±c), Vertices (vertical):(0,±a)\text{Foci (vertical)}: (0, \pm c) \text{, Vertices (vertical)}: (0, \pm a)

💡Examples

Problem 1:

Find the coordinates of the foci and the vertices, the eccentricity, and the length of the latus rectum for the hyperbola x216−y29=1\frac{x^2}{16} - \frac{y^2}{9} = 1.

Solution:

Comparing with x2a2−y2b2=1\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1, we get a2=16a^2 = 16 and b2=9b^2 = 9. Therefore, a=4a = 4 and b=3b = 3. We find c=a2+b2=16+9=25=5c = \sqrt{a^2 + b^2} = \sqrt{16 + 9} = \sqrt{25} = 5.

  1. Vertices: (±a,0)=(±4,0)(\pm a, 0) = (\pm 4, 0)
  2. Foci: (±c,0)=(±5,0)(\pm c, 0) = (\pm 5, 0)
  3. Eccentricity: e=ca=54e = \frac{c}{a} = \frac{5}{4}
  4. Length of Latus Rectum: 2b2a=2(9)4=184=4.5\frac{2b^2}{a} = \frac{2(9)}{4} = \frac{18}{4} = 4.5

Explanation:

Identify the orientation (horizontal since x2x^2 is positive), extract aa and bb, calculate cc using the hyperbola identity, and apply standard coordinate formulae.

Problem 2:

Find the equation of the hyperbola with foci (0,±13)(0, \pm 13) and conjugate axis of length 2424.

Solution:

Since the foci are on the yy-axis, the transverse axis is along the yy-axis. The general equation is y2a2−x2b2=1\frac{y^2}{a^2} - \frac{x^2}{b^2} = 1. Given foci (0,±c)=(0,±13)  ⟹  c=13(0, \pm c) = (0, \pm 13) \implies c = 13. Given length of conjugate axis 2b=24  ⟹  b=122b = 24 \implies b = 12. Using c2=a2+b2c^2 = a^2 + b^2, we have: 132=a2+12213^2 = a^2 + 12^2 169=a2+144169 = a^2 + 144 a2=169−144=25a^2 = 169 - 144 = 25 Therefore, the equation is: y225−x2144=1\frac{y^2}{25} - \frac{x^2}{144} = 1

Explanation:

Determine the orientation from the foci. Use the given conjugate axis length to find bb. Solve for a2a^2 using the relationship between a,b,ca, b, c, then substitute into the vertical hyperbola standard form.

Standard equation of Hyperbola Class 11 Notes & Examples