#### Lesson at a Glance

1. **Circle.** A circle is the locus (path) of a point which moves such that its distance from a given point (called centre of the circle) is constant (called radius of the circle).

2. Equation of the circle having centre (h, k) and radius r is

3. Equation of the circle having centre (0, 0) and radius r is

4. **Concentric circles.** Circles having the same centre are

called concentric circles.

5. **Area of circle** = πr2, where r is the radius of the circle.

6. General form of the equation of the circle is

7. **Parabola.** A parabola is the locus (path) of a point which moves such that its distance from a given point (called focus of the parabola) is equal to its perpendicular distance from a given straight line not passing the focus (called directrix of the parabola).

**8. Summary of the main facts about four parabolas instandard form:**

**9. Ellipse**

An ellipse is the locus of a point P (say) which moves such that the sum of its distances from two given points A and B (say) (called foci of the ellipse) is constant say K (called length of major axis of the ellipse) i.e., PA + PB = K.

**10. Hyperbola**

A hyperbola is the locus of a point P(say) which moves such that the difference of its distances from two given points A and B (say) (called foci of the hyperbola) is constant say K (called length of transverse axis of the hyperbola) i.e., | PA – PB | = K.

11. **Summary of the main facts about two ellipses in standard form:**

12. c2 = a2 – b2 for each of the two forms of the ellipse.

13,** of the main facts about two hyperbolas instandard form:**

14. c2 = a2 + b2 for each of the two forms of the hyperbola.

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