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JEE Maths Notes: Chapter on 3D Geometry (3D Dimensional)

1. Introduction to 3D Geometry

3D Geometry deals with the study of shapes and figures in three-dimensional space. It is a branch of geometry that helps us understand the position, orientation, and distance of objects in three-dimensional space. This section introduces the basic concepts of 3D geometry, including the three axes (x, y, and z) and the coordinate system used to represent points in three-dimensional space. The chapter also discusses the importance of 3D geometry in various real-world applications, such as architecture, physics, and engineering.

2. Cartesian Coordinates in 3D

In this section, the concept of the Cartesian coordinate system is extended to three dimensions. A point in 3D space is represented by an ordered triplet (x, y, z), where x, y, and z are the coordinates along the X-axis, Y-axis, and Z-axis, respectively. The distance between two points, the midpoint of two points, and the section formula in three dimensions are also discussed in this subtopic. These basic concepts form the foundation for understanding geometric shapes in three-dimensional space.

3. Direction Cosines and Direction Ratios

Direction cosines are the cosines of the angles that a line makes with the coordinate axes. In this section, the definition and properties of direction cosines are introduced. The direction ratios are related to the direction cosines, and they help define the orientation of a line in 3D space. This subtopic covers the calculation of direction cosines and direction ratios for lines and their applications in geometry.

4. Equation of a Line in 3D

This section discusses the equation of a line in three-dimensional space. The parametric form and symmetric form of the equation of a line are derived and explained. The vector equation of a line is introduced, and the relationship between the direction ratios and the position vector of a point on the line is explored. Various methods to find the equation of a line passing through two points or parallel to a given vector are also included in this section.

5. Equation of a Plane in 3D

The equation of a plane in three-dimensional space is an important concept in 3D geometry. In this subtopic, the general equation of a plane is introduced, followed by the derivation of the equation from the point-normal form and vector form. The concept of the normal vector and how it relates to the plane is explained. Additionally, the conditions for two planes to be parallel or perpendicular are discussed, along with how to find the equation of a plane passing through three non-collinear points.

6. Angle Between Two Lines in 3D

This section covers the concept of the angle between two lines in three-dimensional space. The formula to calculate the angle between two lines using their direction ratios is derived. The dot product of the direction vectors of the lines is used to compute the cosine of the angle between the lines. The conditions for the lines to be parallel or perpendicular are also explored in this subtopic.

7. Angle Between Two Planes

The angle between two planes is determined by the angle between their normal vectors. In this section, the formula to calculate the angle between two planes is derived using the dot product of the normal vectors. The condition for two planes to be parallel or perpendicular is also explained, along with practical examples to demonstrate the calculation of the angle between two planes.

8. Distance Between a Point and a Plane

This subtopic deals with the calculation of the shortest distance between a point and a plane in 3D space. The formula to find the perpendicular distance from a point to a plane is derived and explained. The concept is applied to various problems where the position of the point and the equation of the plane are given, and students learn how to compute the distance between them.

9. Distance Between Two Parallel Lines

In this section, the formula to calculate the distance between two parallel lines in 3D space is discussed. The vector approach is used to derive the distance between two parallel lines. The formula involves the cross product of vectors, and students are taught how to apply this formula in different scenarios.

10. Shortest Distance Between Two Skew Lines

Skew lines are lines that do not intersect and are not parallel. This subtopic covers the concept of the shortest distance between two skew lines, which is the length of the perpendicular drawn from a point on one line to the other line. The formula to calculate the shortest distance between two skew lines is derived using vector algebra and the cross product.

11. Plane through Three Points in 3D

This section explains how to find the equation of a plane passing through three non-collinear points in three-dimensional space. The concept is developed using vectors, where the position vectors of the points are used to compute two vectors lying on the plane. The cross product of these vectors is used to find the normal vector, which helps in deriving the equation of the plane.

12. Coplanarity of Points

The concept of coplanarity refers to whether a set of points lies on the same plane. This section discusses the conditions for points to be coplanar and the vector method to check if a set of four points is coplanar. The vector approach is used to derive a condition for coplanarity, which is crucial for solving problems involving multiple points in 3D geometry.

13. The Vector Equation of a Plane

The vector equation of a plane is an alternative way to represent the equation of a plane in 3D geometry. In this section, students learn how to derive and use the vector equation of a plane, which involves the position vector of a point on the plane and the normal vector. The vector form is particularly useful when solving problems involving vectors and planes in three-dimensional space.

14. Scalar Triple Product and Applications

The scalar triple product is an important concept in vector algebra used to compute the volume of a parallelepiped formed by three vectors. This section covers the definition and properties of the scalar triple product and its applications in geometry. The scalar triple product is also used to determine the volume of solids and to check the coplanarity of points in 3D space.

15. Conclusion and Key Takeaways

This chapter concludes with a review of the key concepts in 3D Geometry. From understanding the basics of the Cartesian coordinate system in 3D to solving complex problems involving lines, planes, and distances, this chapter provides the foundation needed to tackle advanced problems in JEE Mathematics. Mastering the concepts of direction cosines, the equation of lines and planes, and their applications in real-world scenarios is essential for success in competitive exams like JEE.