Conic Sections: Overview, Questions, Preparation

Conic Sections 2021 ( Conic Sections )

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Rachit Kumar Saxena

Rachit Kumar SaxenaManager-Editorial

Table of Contents
  1. What are Conic Sections?
  2. Weightage of Conic Sections
  3. Illustrated Examples on Conic Sections
  4. FAQs on Conic Section

What are Conic Sections?

Geometric figures like Circle, Hyperbola, Parabola, and Ellipse are referred to as conic sections because they are formed due to the intersection of a plane and a cone.

What is a Circle?

A circle is a figure in which every point is equidistant from the centre. The distance from the centre to any of its points is called a radius.

In general, a circle can be expressed by the following equation:

x2 + y2 + 2gx + 2fy + c = 0

Here, g, c, and f are constants, and the centre of the circle is (-g, -f). The radius of the circle here is r = square root of ( g2 + f2 - c).

If a circle passes through an origin then the equation becomes x2 + y2 + 2gx + 2fy.

What is a Parabola?

A parabola is a curve-like figure on which any point is equidistant from a fixed point called focus and a straight line that is also fixed called the directrix.

A parabola has 4 forms viz. y2 = 4ax, y2 = -4ax, x2 = 4ay, and x2 = -4ay.

What is an Ellipse?

An ellipse looks like a skewed circle and is referred to as a point set wherein the sum of all the points remains constant from 2 fixed points. The standard forms of an ellipse are given below:

(x2/a2) + (y2/b2) = 1 and (x2/b2) + (y2/a2) = 1.

In both these forms, a > b and b2 = a2(1 - e2) where e > 1.

What is a Hyperbola?

A hyperbola is an open curve obtained from the intersection of the circular conic section with a plane. Here, the ratio of the distance of the points remains constant from a point called focus and a line called the directrix. The standard forms of Hyperbola are given below:

(x2/a2) - (y2/b2) = 1 and (y2/a2) - (x2/b2) = 1.

Weightage of Conic Sections

All the conic sections' topics are extensively covered in Class XI and carry a weightage of 4 to 7 marks. It includes MCQ (Multiple Choice Questions), fill in the blanks, short and long answer questions.

Illustrated Examples on Conic Sections

1. Calculate the equation of the circle with the centre at (0, 3) and radius 2.

Solution. The equation of the circle will be (x - 0)2 + (y - 3)2 = (2)2

 x2 + y2 - 4y + 4 = 4

 x2 + y2- 4y = 0.

2. The equation of the parabola is y2 = 20x. Find its focus, latus rectum's length, its axis and equation of the directrix.

Solution. From the general equation y2 = 4ax we get a = 5. Therefore, the length of the latus rectum will be 4a = 4 x 5 = 20.

The coordinate of the focus will be (5, 0), and the equation of the directrix will be x = -5.

The parabola's axis will be y = 0.

3. Find the equation of the ellipse with the centre at the origin and major axis falling on the y-axis going through points (3, 2) and (1, 6).

Solution. The centre is at (0, 0) and the equation of this ellipse is of the below form:

(x2/b2) + (y2/a2) = 1

As it passes through the points (3, 2) and (1, 6) this equation can be written as:

(9/b2) + (4/a2) = 1

Therefore, (1/b2) + (36/a2) = 1

From the above equations we get the values a2 = 40b2 = 10

Therefore, finally the equation becomes,

(x2/10) + (y2/40) = 1.

FAQs on Conic Section

Q: What are the applications of conic sections?

A: Conic sections prove useful while studying 3D Geometry with numerous applications in electronics, architecture, and other fields.

Q: Is every circle an ellipse?

A: Yes, because a circle is a special case of an ellipse with the same distance from the centre for all the points.

Q: Give a real-life example of an ellipse.

A: The route in which the Earth travels around the Sun is elliptical.

Q: Give a real-life example of a hyperbola.

A: An hourglass looks like two hyperbolas next to each other if we ignore its neck.  

Q: Give a real-life example of a parabola.

A: When the water erupts from a fountain and falls back into the pond, it follows a parabolic path.

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