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Ellipses and Hyperbolas

Standard forms and key features of ellipses and hyperbolas

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Ellipses and Hyperbolas

Ellipses

An ellipse is the set of all points where the sum of distances to two foci is constant.

Standard Form (Horizontal Major Axis)

(x−h)2a2+(y−k)2b2=1,a>b\frac{(x - h)^2}{a^2} + \frac{(y - k)^2}{b^2} = 1, \quad a > b

Standard Form (Vertical Major Axis)

(x−h)2b2+(y−k)2a2=1,a>b\frac{(x - h)^2}{b^2} + \frac{(y - k)^2}{a^2} = 1, \quad a > b

Where:

  • (h,k)(h, k) = center
  • aa = semi-major axis (larger value)
  • bb = semi-minor axis (smaller value)
  • cc = distance from center to focus

Key relationship: c2=a2−b2c^2 = a^2 - b^2

Key Features of Ellipse

For horizontal major axis (x−h)2a2+(y−k)2b2=1\frac{(x - h)^2}{a^2} + \frac{(y - k)^2}{b^2} = 1:

  • Center: (h,k)(h, k)
  • Vertices (endpoints of major axis): (h±a,k)(h \pm a, k)
  • Co-vertices (endpoints of minor axis): (h,k±b)(h, k \pm b)
  • Foci: (h±c,k)(h \pm c, k) where c2=a2−b2c^2 = a^2 - b^2
  • Major axis length: 2a2a
  • Minor axis length: 2b2b

For vertical major axis: Swap the roles (vertices on vertical axis)

Eccentricity

e=ca,0<e<1e = \frac{c}{a}, \quad 0 < e < 1

  • ee close to 00: nearly circular
  • ee close to 11: very elongated

Hyperbolas

A hyperbola is the set of all points where the difference of distances to two foci is constant.

Standard Form (Horizontal Transverse Axis)

(x−h)2a2−(y−k)2b2=1\frac{(x - h)^2}{a^2} - \frac{(y - k)^2}{b^2} = 1

Opens left and right.

Standard Form (Vertical Transverse Axis)

(y−k)2a2−(x−h)2b2=1\frac{(y - k)^2}{a^2} - \frac{(x - h)^2}{b^2} = 1

Opens up and down.

Where:

  • (h,k)(h, k) = center
  • aa = distance from center to vertex
  • bb = determines spread of branches
  • cc = distance from center to focus

Key relationship: c2=a2+b2c^2 = a^2 + b^2 (note: plus, not minus!)

Key Features of Hyperbola

For horizontal transverse axis (x−h)2a2−(y−k)2b2=1\frac{(x - h)^2}{a^2} - \frac{(y - k)^2}{b^2} = 1:

  • Center: (h,k)(h, k)
  • Vertices: (h±a,k)(h \pm a, k)
  • Foci: (h±c,k)(h \pm c, k) where c2=a2+b2c^2 = a^2 + b^2
  • Asymptotes: y−k=±ba(x−h)y - k = \pm\frac{b}{a}(x - h)

For vertical transverse axis: Vertices and foci on vertical axis, asymptotes: y−k=±ab(x−h)y - k = \pm\frac{a}{b}(x - h)

Asymptotes

The branches of a hyperbola approach (but never touch) the asymptotes.

Rectangle method:

  1. Draw rectangle with vertices at (h±a,k±b)(h \pm a, k \pm b)
  2. Draw diagonals of rectangle
  3. These diagonals are the asymptotes

Identifying Conic Sections

From the equation Ax2+Bxy+Cy2+Dx+Ey+F=0Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0 (with B=0B = 0):

  • Circle: A=CA = C (and same sign)
  • Ellipse: A≠CA \neq C but same sign
  • Parabola: Either A=0A = 0 or C=0C = 0 (but not both)
  • Hyperbola: AA and CC have opposite signs

Summary Table

ConicStandard Formcc relationshipKey feature
Circle(x−h)2+(y−k)2=r2(x-h)^2 + (y-k)^2 = r^2N/AAll points distance rr from center
Ellipse(x−h)2a2+(y−k)2b2=1\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1c2=a2−b2c^2 = a^2 - b^2Sum of distances to foci = 2a2a
Hyperbola(x−h)2a2−(y−k)2b2=1\frac{(x-h)^2}{a^2} - \frac{(y-k)^2}{b^2} = 1c2=a2+b2c^2 = a^2 + b^2Difference of distances to foci = 2a2a
Parabola(x−h)2=4p(y−k)(x-h)^2 = 4p(y-k)N/ADistance to focus = distance to directrix

📚 Practice Problems

1Problem 1easy

❓ Question:

Find the vertices, co-vertices, and foci of the ellipse (x−2)225+(y+1)29=1\frac{(x - 2)^2}{25} + \frac{(y + 1)^2}{9} = 1.

💡 Show Solution

Identify the ellipse characteristics:

Step 1: Determine orientation:

  • Form: (x−h)2a2+(y−k)2b2=1\frac{(x - h)^2}{a^2} + \frac{(y - k)^2}{b^2} = 1
  • a2=25>b2=9a^2 = 25 > b^2 = 9 → horizontal major axis
  • a=5a = 5, b=3b = 3
  • Center: (h,k)=(2,−1)(h, k) = (2, -1)

Step 2: Find vertices (endpoints of major axis): Vertices are aa units left and right of center: (2±5,−1)=(7,−1) and (−3,−1)(2 \pm 5, -1) = (7, -1) \text{ and } (-3, -1)

Step 3: Find co-vertices (endpoints of minor axis): Co-vertices are bb units up and down from center: (2,−1±3)=(2,2) and (2,−4)(2, -1 \pm 3) = (2, 2) \text{ and } (2, -4)

Step 4: Find foci using c2=a2−b2c^2 = a^2 - b^2: c2=25−9=16c^2 = 25 - 9 = 16 c=4c = 4

Foci are cc units left and right of center: (2±4,−1)=(6,−1) and (−2,−1)(2 \pm 4, -1) = (6, -1) \text{ and } (-2, -1)

Answers:

  • Center: (2,−1)(2, -1)
  • Vertices: (7,−1)(7, -1) and (−3,−1)(-3, -1)
  • Co-vertices: (2,2)(2, 2) and (2,−4)(2, -4)
  • Foci: (6,−1)(6, -1) and (−2,−1)(-2, -1)
  • Major axis length: 2a=102a = 10
  • Minor axis length: 2b=62b = 6

2Problem 2medium

❓ Question:

Find the center, vertices, foci, and asymptotes of the hyperbola (y+3)216−(x−1)29=1\frac{(y + 3)^2}{16} - \frac{(x - 1)^2}{9} = 1.

💡 Show Solution

Identify the hyperbola characteristics:

Step 1: Determine orientation:

  • yy term is positive → vertical transverse axis (opens up and down)
  • a2=16a^2 = 16, so a=4a = 4
  • b2=9b^2 = 9, so b=3b = 3
  • Center: (h,k)=(1,−3)(h, k) = (1, -3)

Step 2: Find vertices: Vertices are aa units above and below center: (1,−3±4)=(1,1) and (1,−7)(1, -3 \pm 4) = (1, 1) \text{ and } (1, -7)

Step 3: Find foci using c2=a2+b2c^2 = a^2 + b^2: c2=16+9=25c^2 = 16 + 9 = 25 c=5c = 5

Foci are cc units above and below center: (1,−3±5)=(1,2) and (1,−8)(1, -3 \pm 5) = (1, 2) \text{ and } (1, -8)

Step 4: Find asymptotes: For vertical hyperbola: y−k=±ab(x−h)y - k = \pm\frac{a}{b}(x - h) y−(−3)=±43(x−1)y - (-3) = \pm\frac{4}{3}(x - 1) y+3=±43(x−1)y + 3 = \pm\frac{4}{3}(x - 1)

Two asymptotes: y=43(x−1)−3=43x−133y = \frac{4}{3}(x - 1) - 3 = \frac{4}{3}x - \frac{13}{3} y=−43(x−1)−3=−43x−53y = -\frac{4}{3}(x - 1) - 3 = -\frac{4}{3}x - \frac{5}{3}

Answers:

  • Center: (1,−3)(1, -3)
  • Vertices: (1,1)(1, 1) and (1,−7)(1, -7)
  • Foci: (1,2)(1, 2) and (1,−8)(1, -8)
  • Asymptotes: y=43x−133y = \frac{4}{3}x - \frac{13}{3} and y=−43x−53y = -\frac{4}{3}x - \frac{5}{3}

3Problem 3hard

❓ Question:

Write the equation of an ellipse with center at the origin, a focus at (0,3)(0, 3), and a vertex at (0,5)(0, 5).

💡 Show Solution

Determine ellipse characteristics:

Step 1: Analyze given information:

  • Center: (0,0)(0, 0)
  • Focus: (0,3)(0, 3) → on yy-axis → vertical major axis
  • Vertex: (0,5)(0, 5) → also on yy-axis ✓

Step 2: Find aa and cc:

  • Distance from center to vertex: a=5a = 5
  • Distance from center to focus: c=3c = 3

Step 3: Use c2=a2−b2c^2 = a^2 - b^2 to find bb: 32=52−b23^2 = 5^2 - b^2 9=25−b29 = 25 - b^2 b2=16b^2 = 16 b=4b = 4

Step 4: Write equation (vertical major axis with center at origin): x2b2+y2a2=1\frac{x^2}{b^2} + \frac{y^2}{a^2} = 1 x216+y225=1\frac{x^2}{16} + \frac{y^2}{25} = 1

Step 5: Verify:

  • Center: (0,0)(0, 0) ✓
  • a=5a = 5, so vertices: (0,±5)(0, \pm 5) ✓
  • c=3c = 3, so foci: (0,±3)(0, \pm 3) ✓
  • b=4b = 4, so co-vertices: (±4,0)(\pm 4, 0)

Answer: x216+y225=1\frac{x^2}{16} + \frac{y^2}{25} = 1

4Problem 4medium

❓ Question:

Find the center, vertices, and foci of the ellipse: (x - 1)²/25 + (y + 2)²/9 = 1

💡 Show Solution

Step 1: Identify the center: Standard form: (x - h)²/a² + (y - k)²/b² = 1 Center: (h, k) = (1, -2)

Step 2: Identify a² and b²: a² = 25, so a = 5 b² = 9, so b = 3

Step 3: Determine major axis: Since a² > b², major axis is horizontal

Step 4: Find vertices (on major axis): Vertices are a units left and right of center (1 - 5, -2) = (-4, -2) (1 + 5, -2) = (6, -2)

Step 5: Find c using c² = a² - b²: c² = 25 - 9 = 16 c = 4

Step 6: Find foci (on major axis): Foci are c units from center along major axis (1 - 4, -2) = (-3, -2) (1 + 4, -2) = (5, -2)

Answer: Center (1, -2), Vertices (-4, -2) and (6, -2), Foci (-3, -2) and (5, -2)

5Problem 5hard

❓ Question:

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

💡 Show Solution

Step 1: Determine orientation: Vertices and foci on x-axis → horizontal hyperbola Standard form: x²/a² - y²/b² = 1

Step 2: Find a from vertices: Vertices at (±a, 0) = (±3, 0) a = 3, so a² = 9

Step 3: Find c from foci: Foci at (±c, 0) = (±5, 0) c = 5

Step 4: Find b using c² = a² + b²: 5² = 3² + b² 25 = 9 + b² b² = 16 b = 4

Step 5: Write the equation: x²/9 - y²/16 = 1

Step 6: Find asymptotes (for reference): y = ±(b/a)x = ±(4/3)x

Answer: x²/9 - y²/16 = 1

Explain using:

⚠️ Common Mistakes: Ellipses and Hyperbolas

Avoid these 4 frequent errors

🌍 Real-World Applications: Ellipses and Hyperbolas

See how this math is used in the real world

📝 Worked Example: Related Rates — Expanding Circle

Problem:

A stone is dropped into a still pond, creating a circular ripple. The radius of the ripple is increasing at a rate of 22 cm/s. How fast is the area of the circle increasing when the radius is 1010 cm?

2Write the relationship between variables
3Differentiate both sides with respect to time
4Substitute known values

📌 Related Topics in Function Fundamentals

❓ Frequently Asked Questions

What is Ellipses and Hyperbolas?▾
Standard forms and key features of ellipses and hyperbolas
How can I study Ellipses and Hyperbolas effectively?▾
Start by reading the study notes and working through the examples on this page. Then use the flashcards to test your recall. Practice with the 5 problems provided, checking solutions as you go. Regular review and active practice are key to retention.
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Ellipses and Hyperbolas is part of the AP Precalculus course on Study Mondo, specifically in the Function Fundamentals section. You can explore the full course for more related topics and practice resources.
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Yes, this page includes 5 practice problems with detailed solutions. Each problem includes a step-by-step explanation to help you understand the approach.