EAPCET Mathematics · Intermediate second year · Paper IIB

Ellipse

Ellipse covers the standard ellipse, its eccentricity, foci and directrices, the latus rectum, and tangent conditions.

Subject
Mathematics
Taught in
Intermediate second year · Paper IIB
Mathematics in the paper
80 of 160 questions

Key formulas and results

  • x2a2+y2b2=1\dfrac{x^{2}}{a^{2}} + \dfrac{y^{2}}{b^{2}} = 1 (a>b)(a > b): b2=a2(1−e2)b^{2} = a^{2}(1 - e^{2})
  • Foci (±ae,0)(\pm ae, 0) and directrices x=±aex = \pm\dfrac{a}{e}
  • Latus rectum length =2b2a= \dfrac{2b^{2}}{a}
  • y=mx+cy = mx + c touches the ellipse iff c2=a2m2+b2c^{2} = a^{2}m^{2} + b^{2}
  • Parametric point: (acos⁡θ,bsin⁡θ)(a\cos\theta, b\sin\theta)
  • Sum of the focal distances of any point =2a= 2a
  • Point of contact of the tangent y=mx+cy = mx + c with x2a2+y2b2=1\dfrac{x^{2}}{a^{2}} + \dfrac{y^{2}}{b^{2}} = 1: (−a2mc,b2c)\left(-\dfrac{a^{2}m}{c}, \dfrac{b^{2}}{c}\right)
  • Area enclosed by the ellipse x2a2+y2b2=1\dfrac{x^{2}}{a^{2}} + \dfrac{y^{2}}{b^{2}} = 1: πab\pi ab

What this chapter covers

  • Standard equation
  • Eccentricity, foci and directrices
  • Latus rectum
  • Parametric form
  • Tangents and normals

How it is usually asked

  • Find the eccentricity or foci
  • Write the equation from given data
  • Apply the tangent condition

Understanding Ellipse

An ellipse is the set of points whose distance from a focus is e times the distance from the matching directrix, with 0 < e < 1. Equivalently, the sum of the distances of any point from the two foci is constant, equal to the length of the major axis. In standard form x²/a² + y²/b² = 1 with a > b, the major axis lies along the x-axis and b² = a²(1 − e²).

From a and e everything else follows. The foci are (±ae, 0), the directrices are x = ±a/e, the vertices are (±a, 0) and the latus rectum has length 2b²/a. If instead b > a, the major axis lies along the y-axis and the roles of a and b swap, so the foci move to the y-axis. Always check which denominator is larger before using any formula.

Points on the ellipse can be written as (a cos θ, b sin θ), which simplifies tangent and normal questions. The line y = mx + c touches the ellipse when c² = a²m² + b², and the tangent at (x₁, y₁) is xx₁/a² + yy₁/b² = 1. EAPCET questions ask for eccentricity, foci, latus rectum, an equation from given data or a tangent condition.

Worked example

EAPCET-style question

The foci of the ellipse 4x2+3y2=124x^{2} + 3y^{2} = 12 are

  1. (1)(±1,0)(\pm 1, 0)
  2. (2)(0,±1)(0, \pm 1)
  3. (3)(0,±2)(0, \pm 2)
  4. (4)(±7,0)(\pm\sqrt{7}, 0)

Solution

  1. Divide by 12: x23+y24=1\dfrac{x^{2}}{3} + \dfrac{y^{2}}{4} = 1.
  2. The larger denominator 4 is under y2y^{2}, so the major axis is along the yy-axis with semi-major axis 2 and semi-minor axis 3\sqrt{3}.
  3. Distance from centre to each focus =4−3=1= \sqrt{4 - 3} = 1, so e=12e = \tfrac{1}{2}.
  4. The foci are (0,±1)(0, \pm 1).

Answer: (0,±1)(0, \pm 1)

More practice questions

Practice question 1

The area enclosed by the ellipse 9x2+16y2=1449x^{2} + 16y^{2} = 144 is

  1. (1)12π12\pi
  2. (2)24π24\pi
  3. (3)144π144\pi
  4. (4)7π7\pi

Solution

  1. Divide by 144: x216+y29=1\dfrac{x^{2}}{16} + \dfrac{y^{2}}{9} = 1
  2. a=4a = 4 and b=3b = 3
  3. Area =πab=12π= \pi ab = 12\pi

Answer: 12π12\pi

Common mistakes to avoid

  • Assuming the major axis is along the x-axis; compare the denominators after making the right side 1.
  • Reading a and b before dividing the equation to get 1 on the right side.
  • Using b² = a²(e² − 1), the hyperbola relation; for an ellipse b² = a²(1 − e²), so e is always less than 1.
  • Taking the latus rectum as 2a²/b; it is 2b²/a, with a the semi-major axis.

How to prepare it

Check whether the major axis is along x or y before using any formula.

Once the formulas feel familiar, test them the way the exam does: practise Ellipse questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Mathematics chapters

See every chapter in the EAPCET Mathematics syllabus.

Practise Ellipse chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is Ellipse part of the EAPCET Mathematics syllabus?
Yes. Ellipse is taught in Intermediate second year · Paper IIB Mathematics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare Ellipse for EAPCET?
Check whether the major axis is along x or y before using any formula.
How many Mathematics questions are there in EAPCET?
80 of the 160 questions in the Engineering paper are Mathematics, spread across 37 chapters.
What mistakes do students make in Ellipse?
Assuming the major axis is along the x-axis; compare the denominators after making the right side 1. Reading a and b before dividing the equation to get 1 on the right side. Using b² = a²(e² − 1), the hyperbola relation; for an ellipse b² = a²(1 − e²), so e is always less than 1. Taking the latus rectum as 2a²/b; it is 2b²/a, with a the semi-major axis.