Chapter 27-Hyperbola


Introduction to Hyperbola - Class 11 Maths

The hyperbola is one of the most important topics in RD Sharma Solutions Class 11 Mathematics under the conic sections chapter. This comprehensive guide provides detailed RD Sharma solutions, covering all essential concepts, formulas, and problem-solving techniques that students need to excel in their CBSE examinations.

A hyperbola is defined as the locus of a point that moves in a plane such that the difference of its distances from two fixed points (called foci) remains constant. This constant difference is always less than the distance between the two foci. Understanding hyperbolas is crucial not only for board examinations but also for competitive exams like JEE and other engineering entrance tests.

What is a Hyperbola?

Definition and Basic Concept

A hyperbola is a type of conic section formed when a plane intersects both nappes (the upper and lower cones) of a double cone. Mathematically, a hyperbola is the set of all points P in a plane such that the absolute difference of distances from two fixed points F₁ and F₂ (foci) is constant.

Mathematical Definition: |PF₁ - PF₂| = 2a, where 2a < F₁F₂

Components of a Hyperbola

  • Foci (F₁ and F₂): Two fixed points that define the hyperbola
  • Center (C): The midpoint of the line segment joining the two foci
  • Transverse Axis: The line segment joining the two vertices, passing through the foci
  • Conjugate Axis: The line perpendicular to the transverse axis passing through the center
  • Vertices (A and A'): Points where the hyperbola intersects the transverse axis
  • Eccentricity (e): A measure of how "stretched" the hyperbola is (e > 1 for hyperbolas)
  • Asymptotes: Lines that the hyperbola approaches but never touches

Formulas for Hyperbola Class 11

Understanding and memorizing these formulas is essential for solving hyperbola problems effectively. Here's a comprehensive table of all important formulas:

Formula Name Mathematical Expression Explanation
Standard Equation (Horizontal) x²/a² - y²/b² = 1 Hyperbola with transverse axis along x-axis
Standard Equation (Vertical) y²/a² - x²/b² = 1 Hyperbola with transverse axis along y-axis
Relationship between a, b, c c² = a² + b² Connects semi-axes with focal distance
Eccentricity e = c/a or e = √(1 + b²/a²) Always greater than 1 for hyperbolas
Coordinates of Foci (Horizontal) (±c, 0) or (±ae, 0) Location of focal points
Coordinates of Foci (Vertical) (0, ±c) or (0, ±ae) Location of focal points
Coordinates of Vertices (Horizontal) (±a, 0) Points where hyperbola intersects x-axis
Coordinates of Vertices (Vertical) (0, ±a) Points where hyperbola intersects y-axis
Length of Transverse Axis 2a Distance between two vertices
Length of Conjugate Axis 2b Length perpendicular to transverse axis
Length of Latus Rectum 2b²/a Focal chord perpendicular to transverse axis
Equation of Asymptotes (Horizontal) y = ±(b/a)x Lines approached by hyperbola branches
Equation of Asymptotes (Vertical) y = ±(a/b)x Lines approached by hyperbola branches
Directrix Equation (Horizontal) x = ±a/e Fixed lines used in focus-directrix definition
Directrix Equation (Vertical) y = ±a/e Fixed lines used in focus-directrix definition
Focal Distance Formula PF₁ - PF₂ = ±2a Difference of distances from any point to foci

Additional Important Relationships

  • Parametric Equations (Horizontal): x = a sec θ, y = b tan θ
  • Parametric Equations (Vertical): x = b tan θ, y = a sec θ
  • Rectangular Hyperbola: xy = c² (when asymptotes are coordinate axes)
  • Conjugate Hyperbola: If x²/a² - y²/b² = 1 is a hyperbola, then x²/a² - y²/b² = -1 is its conjugate

Stepwise Method to Convert General to Standard Hyperbola Equation

Converting a general second-degree equation into standard form is a crucial skill for solving hyperbola problems. Follow this systematic approach:

Step 1: Identify the General Form

The general equation of a conic section is: Ax² + Bxy + Cy² + Dx + Ey + F = 0

For a hyperbola, the condition is: B² - 4AC > 0 (and B = 0 for axes parallel to coordinate axes)

Step 2: Group Terms by Variable

Rearrange the equation by grouping x-terms and y-terms together:

  • Move all x² and x terms together
  • Move all y² and y terms together
  • Keep the constant on the right side

Step 3: Complete the Square

For both x and y variables, complete the square:

For x terms: Ax² + Dx

  • Factor out A: A(x² + D/A·x)
  • Add and subtract (D/2A)²: A[x² + D/A·x + (D/2A)² - (D/2A)²]
  • Simplify: A[(x + D/2A)² - (D/2A)²]

For y terms: Cy² + Ey

  • Follow the same process with C and E

Step 4: Simplify and Rearrange

After completing the square, simplify the equation and move constants to the right side.

Step 5: Convert to Standard Form

Divide the entire equation by the constant on the right side to get 1 on the right:

(x - h)²/a² - (y - k)²/b² = 1 (horizontal hyperbola)

or

(y - k)²/a² - (x - h)²/b² = 1 (vertical hyperbola)

Where (h, k) is the center of the hyperbola.

Practical Example

Problem: Convert 9x² - 16y² - 18x + 32y - 151 = 0 to standard form

Solution:

Step 1: Group terms 9x² - 18x - 16y² + 32y = 151

Step 2: Factor out coefficients 9(x² - 2x) - 16(y² - 2y) = 151

Step 3: Complete the square 9(x² - 2x + 1 - 1) - 16(y² - 2y + 1 - 1) = 151 9[(x - 1)² - 1] - 16[(y - 1)² - 1] = 151 9(x - 1)² - 9 - 16(y - 1)² + 16 = 151

Step 4: Simplify 9(x - 1)² - 16(y - 1)² = 151 + 9 - 16 9(x - 1)² - 16(y - 1)² = 144

Step 5: Divide by 144 (x - 1)²/16 - (y - 1)²/9 = 1

This is a horizontal hyperbola with center (1, 1), a² = 16, b² = 9.

Important Solved Examples from RD Sharma Hyperbola Chapter

Example 1: Finding the Equation of a Hyperbola

Problem: Find the equation of the hyperbola with foci at (±5, 0) and vertices at (±3, 0).

Solution:

Given:

  • Foci: (±5, 0) → c = 5
  • Vertices: (±3, 0) → a = 3

Using the relation c² = a² + b²:

  • 25 = 9 + b²
  • b² = 16
  • b = 4

Since the foci lie on the x-axis, the equation is: x²/9 - y²/16 = 1

Verification:

  • Eccentricity e = c/a = 5/3 > 1 ✓
  • Length of transverse axis = 2a = 6
  • Length of conjugate axis = 2b = 8

Example 2: Finding Eccentricity

Problem: Find the eccentricity of the hyperbola 16x² - 9y² = 144.

Solution:

Step 1: Convert to standard form 16x² - 9y² = 144 x²/9 - y²/16 = 1

Step 2: Identify a² and b²

  • a² = 9 → a = 3
  • b² = 16 → b = 4

Step 3: Calculate eccentricity Using e = √(1 + b²/a²): e = √(1 + 16/9) e = √(25/9) e = 5/3

Alternative method: c² = a² + b² = 9 + 16 = 25 → c = 5 e = c/a = 5/3

Example 3: Finding Foci and Asymptotes

Problem: For the hyperbola 4x² - 9y² = 36, find: (a) Coordinates of foci (b) Equations of asymptotes (c) Length of latus rectum

Solution:

Convert to standard form: x²/9 - y²/4 = 1

Here, a² = 9 (a = 3) and b² = 4 (b = 2)

(a) Coordinates of foci:

  • c² = a² + b² = 9 + 4 = 13
  • c = √13
  • Foci: (±√13, 0)

(b) Equations of asymptotes: For x²/a² - y²/b² = 1, asymptotes are y = ±(b/a)x

  • y = ±(2/3)x
  • Or: 2x - 3y = 0 and 2x + 3y = 0

(c) Length of latus rectum:

  • Length = 2b²/a = 2(4)/3
  • Length = 8/3 units

Example 4: Point on Hyperbola

Problem: Show that the point (3√2, 2) lies on the hyperbola x²/9 - y²/4 = 1.

Solution:

Substitute x = 3√2 and y = 2 into the equation:

LHS = (3√2)²/9 - (2)²/4 = 18/9 - 4/4 = 2 - 1 = 1 = RHS

Since LHS = RHS, the point (3√2, 2) lies on the hyperbola. ✓

Example 5: Finding the Equation with Given Properties

Problem: Find the equation of the hyperbola whose eccentricity is 2 and the distance between the foci is 16.

Solution:

Given:

  • e = 2
  • Distance between foci = 2c = 16 → c = 8

Using e = c/a:

  • 2 = 8/a
  • a = 4

Using c² = a² + b²:

  • 64 = 16 + b²
  • b² = 48

Since no specific orientation is given, we can write both forms:

Horizontal hyperbola: x²/16 - y²/48 = 1

Vertical hyperbola: y²/16 - x²/48 = 1

Example 6: Conjugate Hyperbola

Problem: Find the equation of the conjugate hyperbola of x²/25 - y²/16 = 1.

Solution:

For a hyperbola x²/a² - y²/b² = 1, the conjugate hyperbola is: x²/a² - y²/b² = -1

Or equivalently: -x²/a² + y²/b² = 1, which is y²/b² - x²/a² = 1

Therefore, the conjugate hyperbola is: y²/16 - x²/25 = 1

Properties comparison:

  • Original: Transverse axis along x-axis, a = 5, b = 4
  • Conjugate: Transverse axis along y-axis, a = 4, b = 5
  • Both share the same asymptotes: y = ±(4/5)x

List of Common Mistakes Students Make on Hyperbola Problems

Understanding common errors helps students avoid them and improve their problem-solving accuracy. Here are the most frequent mistakes:

1. Confusing Hyperbola with Ellipse Formulas

Mistake: Using c² = a² - b² (ellipse formula) instead of c² = a² + b² (hyperbola formula)

Why it happens: Students mix up conic section formulas

How to avoid: Remember that for hyperbolas, c is always greater than a, so c² = a² + b² (addition). For ellipses, c < a, so c² = a² - b² (subtraction).

2. Incorrect Eccentricity Range

Mistake: Stating e < 1 for hyperbolas or forgetting that e > 1 always

Why it happens: Confusion between different conic sections

How to avoid: Memorize: Circle (e = 0), Ellipse (0 < e < 1), Parabola (e = 1), Hyperbola (e > 1)

3. Wrong Identification of Transverse Axis

Mistake: Not recognizing whether the hyperbola opens horizontally or vertically

Why it happens: Not paying attention to which term is positive in the standard equation

How to avoid: In standard form, the positive term indicates the direction of the transverse axis:

  • x²/a² - y²/b² = 1 → horizontal (opens left-right)
  • y²/a² - x²/b² = 1 → vertical (opens up-down)

4. Incorrect Asymptote Equations

Mistake: Writing asymptotes as y = ±(a/b)x for all hyperbolas

Why it happens: Not considering the orientation of the hyperbola

How to avoid:

  • For x²/a² - y²/b² = 1: asymptotes are y = ±(b/a)x
  • For y²/a² - x²/b² = 1: asymptotes are y = ±(a/b)x
  • Remember: divide by the coefficient of x in the asymptote equation

5. Calculation Errors in Completing the Square

Mistake: Incorrect arithmetic when completing the square or forgetting to balance both sides

Why it happens: Rushing through algebraic steps

How to avoid: Work methodically, add/subtract the same value, and verify each step

6. Misplacing the Center

Mistake: Assuming the center is always at the origin

Why it happens: Only practicing standard position problems

How to avoid: Always check if the equation is in the form (x-h)²/a² - (y-k)²/b² = 1, where (h,k) is the center

7. Wrong Latus Rectum Formula

Mistake: Using 2a²/b instead of 2b²/a

Why it happens: Mixing up the numerator and denominator

How to avoid: Remember: latus rectum = 2b²/a (b² on top, a on bottom)

8. Sign Errors in General Equation

Mistake: Dropping or changing signs when expanding or simplifying

Why it happens: Careless calculation

How to avoid: Double-check every step, especially when moving terms across the equals sign

9. Forgetting to Check Domain/Range

Mistake: Not verifying that points satisfy the constraints of the hyperbola

Why it happens: Not understanding the geometric nature of hyperbolas

How to avoid: For x²/a² - y²/b² = 1, remember x ≥ a or x ≤ -a; y can be any real number

10. Incorrect Directrix Calculation

Mistake: Using x = ±ae instead of x = ±a/e for directrix

Why it happens: Confusion with focus calculation

How to avoid: Remember: foci are at ±ae (multiply), directrices are at ±a/e (divide)

Step-by-Step Problem-Solving Strategy for Hyperbola Questions

General Approach

  1. Read the problem carefully and identify what is given and what is to be found
  2. Sketch a diagram whenever possible to visualize the hyperbola
  3. Identify the type of hyperbola (horizontal or vertical)
  4. List known values and formulas that might be needed
  5. Apply formulas systematically and show all work
  6. Verify your answer by substituting back or checking logical consistency

Tips for Exam Success

  • Practice converting between different forms of hyperbola equations
  • Memorize standard formulas and their derivations
  • Work through RD Sharma exercise problems systematically
  • Focus on conceptual understanding, not just formula memorization
  • Time yourself while solving problems to improve speed
  • Review common mistakes before exams

Practice Questions (with Hints)

Question 1

Find the equation of the hyperbola with center at origin, length of transverse axis 12, and eccentricity 5/3.

Hint: Use 2a = 12 to find a, then use e = c/a to find c, finally use c² = a² + b².

Question 2

Find the coordinates of foci, vertices, length of latus rectum, and eccentricity of the hyperbola 9y² - 4x² = 36.

Hint: First convert to standard form by dividing throughout by 36.

Question 3

Show that the line 3x - 4y = 7 touches the hyperbola 4x² - 9y² = 36.

Hint: Substitute y = (3x-7)/4 into the hyperbola equation and check if discriminant = 0.

Question 4

Find the equation of the hyperbola whose foci are (0, ±√10) and passing through the point (2, 3).

Hint: Since foci are on y-axis, use y²/a² - x²/b² = 1, and use c² = a² + b² with c = √10.

Downloadable PDF Notes for Class 11 Hyperbola Chapter

What's Included in the PDF

Our comprehensive PDF notes include:

  1. Complete theory coverage with definitions and concepts
  2. All important formulas in consolidated tables
  3. Step-by-step solved examples from RD Sharma
  4. Practice problems with varying difficulty levels
  5. Quick revision notes for last-minute preparation
  6. Graphical representations of different types of hyperbolas
  7. Comparison charts between different conic sections
  8. Common mistakes checklist to avoid errors
  9. Previous year question papers analysis
  10. Tips and tricks for competitive exam preparation

How to Use These Notes Effectively

  • Start with theory: Read through concepts thoroughly before attempting problems
  • Practice regularly: Solve at least 5-10 problems daily
  • Mark difficult questions: Revisit challenging problems periodically
  • Create a formula sheet: Write formulas by hand for better retention
  • Solve previous years' papers: Understand exam patterns and question types
  • Group study: Discuss difficult concepts with classmates
  • Seek help promptly: Don't let doubts accumulate

Additional Resources

For complete mastery of the hyperbola chapter, students should:

Conclusion

Mastering hyperbolas requires consistent practice, strong conceptual understanding, and familiarity with various problem types. This guide provides comprehensive coverage of the RD Sharma Class 11 Hyperbola chapter, including all essential formulas, solved examples, and common pitfalls to avoid.

Important Notes:

  • Understand the geometric definition and properties
  • Memorize standard formulas and their applications
  • Practice conversion between general and standard forms
  • Learn to identify hyperbola orientation quickly
  • Avoid common mistakes through awareness
  • Solve diverse problems regularly

Remember that hyperbolas form a crucial foundation for advanced mathematics and appear frequently in JEE and other competitive examinations. Invest time in understanding the concepts deeply rather than just memorizing formulas.

Download our comprehensive PDF notes to access detailed explanations, additional practice problems, and quick revision material that will help you excel in your Class 11 CBSE Mathematics examination.

RD Sharma Class 11 Maths Hyperbola Solutions - Chapter Notes & PDF Download