3D geometry and vectors were introduced in Maths to help students grasp different types of shapes and figures. Almost all items in the real world have three dimensions. Many household items, for example, contain 3D geometry, such as pens, laptops, windows, culinary utensils, and so on. Students have studied the fundamentals of three-dimensional geometry in class 11. In class 12, the advanced version of 3-D geometry is taught. Vector algebra will now be applied to three-dimensional geometry.

The goal of this 3-dimensional geometry approach is to create a simple yet elegant study structure. Important concepts covered in three-dimensional geometry for Class 12 include direction cosine and direction ratios of a line connecting two points. The notes are based on the term 2 CBSE and NCERT syllabuses.

Students can review Maths Chapter 11 (Three-dimensional geometry) with notes created according to the most recent exam pattern. The students will also study the equations of lines and planes in space under various conditions, the angle between a line and a plane, and the angle between two lines, among other things. To better understand the material, you should practise the problems based on the NCERT solutions for class 12 Maths. This chapter has great importance in exams like JEE 2022, JEE Advanced 2022, National Engineering Olympiad, and other olympiads in India.

Table of Contents |
---|

Important Notes |

Line Equations |

Plane Equations |

Conclusion |

FAQs |

**Important Notes**

A student preparing for CBSE 12th Maths term two examinations ought to study the notes mentioned below in this article. These notes are created by subject experts and toppers who are well versed with the examination pattern. Since this term’s paper is subjective, there are chances that at least two questions out of four long answer-type questions will come from this chapter. Hence it is important to go through each note mentioned in the article.

**Direction Cosine and Direction Ratio**

The direction cosine and direction ratios are the first things taught in CBSE 12th 3D geometry. These can be understood by making a line pass through the origin (0,0). Let angles formed by the line and axes be α, β, γ with x, y, and z-axes. Therefore finding the cosine of these angles will give us the direction cosine of the line. For now, let us consider the

x = ka

y = kb

z = kc

xa = yb = zc = k

Therefore the direction cosines will be formulated as:

m = ± a2/ √(a2 + b2 + c2)

m = ± b2/ √(a2 + b2 + c2)

m = ± c2/ √(a2 + b2 + c2)

Note that two parallel lines have the same set direction cosines if we are provided with a line that doesn’t pass through the origin. The students need to create a new line from the origin parallel to the given line. Now you can find the direction cosines of the new line, which will be the same as the original line.

The relation between the direction cosines is that the sum of squares of the direction cosines must be equal to one. For the line having direction cosines x, y, and z, the relation is

x2 + y2 + z2 = 1

**Direction Cosine For a Line Between Two Points**

Suppose there is a line RS such that R(a1, b1, c1) and S(a2, b2, c2). The direction cosine between these points is formulated as:

x = a2 – a1/ RS

y = b2 – b1/ RS

z = c2 – c1/ RS

Here RS = √ (a2 – a1)2 + (b2 – b1)2 + (c2 – c1)2

**Line Equations **

**Equation Of a Line in 3D Space**** **

The equation of a line can be determined in two ways

- If the direction of the line along with the point through which it passes is given.
- The line passed from two known points.

**Equation of a line through a point parallel to a given vector**

* Vector Form: *

The equation of the line in vector form is given by the formula

r= x + λy

Where r = the vector of the arbitrary position of a point on the line

x = the position vector of any point A

y = the vector parallel to x

λ = Any real number

*Cartesian Form:*

The equation of the line in vector form is given by the formula

(x – x1)/ a = (y – y1)/ b = (z – z1)/ c

Where (x1, y1, z1) are the coordinates of the known point and (a, b, c) are the direction cosines of the line.

**Equation of a line through a point parallel to a given vector**

*Vector Form:*

The equation of the line in vector form is given by the formula

r= x + λ(y – x)

Where r = the vector of the arbitrary position of a point on the line

x = the position vector of any point A

y = the vector parallel to x

λ = Any real number

*Cartesian Form:*

The equation of the line in vector form is given by the formula

(x – x1)/ (x2 – x1) = (y – y1)/ (y2 – y1) = (z – z1)/(z2 – z1)

The above equation is also known as the standard cartesian equation of a line where (x1, y1, z1) and (x2, y2, z2) are the coordinates of the known points.

**Angle Between Two Lines**

Consider two lines L1 and L2 having direction cosines as (x1, y1, z1) and (x2, y2, z2) respectively. The angle formed between the two line is determined by using the formula:

Cos θ = (x1x2 + y1y2 + z1z2) / (√x12 + y12 + z12 . √x22 + y22 + z22)

Here x1i + y1j + z1k and x2i + y2j + z2k are two vectors intersecting at a point A.

*Special Cases:*

- When the lines are perpendicular → x1x2 + y1y2 + z1z2 = 0
- When the lines are parallel to each other → x1/x2 = y1/y2 = z1/z2

**Shortest Distance Between Two Lines**

The shortest distance between lines L1 and L2 given by the formulas r= x1 + λy1 and r= x2 + y2 is formulated as:

D = Modulus [ (y1 ⨯ y2) . (x1⨯ x2) / |(y1 ⨯ y2)| ]

**Plane Equations **

**Equation of a Plane in 3D**

The equation of a plane in 3D geometry is given by the matrix:

A =

This matrix is equal to zero. A = 0.

The vector form of a plane in the normal form is given as:

- r. n = d. Here vector r is the position vector of a point on the plane, ‘n’ is the normal and d is the length covered by the normal from the origin to the plane.

The cartesian form of a plane is lx + my + nz + d = 0 for any point P(x,y,z) having direction cosines l, m, and n.

**Intercept Formula of a Plane**

The formula of a plane passing through the points (a,0,0), (0, b, 0), and (0,0,c) is given as:

xa + yb + zc = 1

**Coplanarity of Two Lines**

Two lines are said to lie on the same plane if line 1 = x1 +λy1 and line 2 = x2 +y2 are such that (x1 – x2). (y1 ⨯ y2) = 0.

**Angle Between Two Planes**

The angle between two planes A and B having normal form equation as r. n1 = d1 and r. n2 = d2 is given by the formula:

** Vector form**: Cos θ = |n1.n2||n1|.|n2|

** Cartesian Form: **Cos θ = Modulus [ (x1x2 + y1y2 + z1z2) / (√x12 + y12 + z12 . √x22 + y22 + z22)]. Here (x1, y1, z1) and (x2, y2, z2) are the direction ratios of the planes.

**Equation Of a Plane Through The Intersection of Two Planes**

*Vector Equation*

Let the two planes be X and Y with the vector formula r. n1 = d1 and r. n2 = d2 respectively. The vector equation for plane passing through the intersection of two planes is:

- r. (n1 + λn2) = d1 +λd2

*Cartesian Equation *

The cartesian equation of a plane which passes through the intersection of two given planes P1x + Q1y + R1z + S1 = 0 and P2x + Q2y + R2z + S2 = 0 is formulated as (P1x + Q1y + R1z + S1) + λ(P2x + Q2y + R2z + S2) = 0.

**Distance Between a Point And Plane**

The distance between a point X (k, l, m) from a plane Ax + By + Cz = D is given as

D = Modulus [(Ak + Bl + Cm – D) / (√A2 + B2 + C2)]

**Conclusion**

3D geometry and vectors is a formula-based chapter. A student may find this hard due to the plethora of formulas and Maths concepts. Once a student gets an idea about how the formulas were derived, they can easily understand the ideas of this chapter. There are short as well as long formulas in this chapter. All of them are necessary for CBSE boards and JEE 2022 and other olympiad exams 2021-22. Long answer-type questions will appear in this chapter, so a student must be well prepared with all the topics and formulas. Every question in the NCERT Solutions for class 12 must be solved twice to increase the speed of the final examination. A student must seek help from teachers or NCERT solutions for 3D geometry for answers to the problems. They can also look for problems in previous year’s question papers and solve them to achieve a better score.

**FAQs**

** 1. What major topics may appear in CBSE 12th Maths term two exams from 3D geometry and vectors?**

Class 12 Chapter 11 “3D Geometry” Maths is all about direction cosines, vectors. Most pupils can be extremely perplexing if the fundamentals are not well grasped. Revision Notes, which are available here, can assist students in understanding subjects. The below-mentioned topics might appear on your test. Experts speculate on these, so keep a major focus on them. The topics are:

- Distance formula and coordinates
- Cosines and ratios in one direction
- Lines intersecting and angles formed between them
- Shortest distance and skew lines
- Lines and planes equations
- Intersections and the angle formed between two planes

**2. ****How can a student use Aakash’s Notes to prepare for 3D geometry and vectors**

Students can master important concepts of the chapter on 3D Geometry by using Aakash’s Notes for Class 12 Chapter 11. The chapter can be rather perplexing if the essential concepts are not grasped. These notes can assist students, as professionals write the answers to most tasks. The key formulae are provided so that students can quickly grasp them, prepare properly, and achieve good results on their exams. A student doesn’t search 100 pages for an answer. Using Aakash’s notes, they can easily find all the formulas in one article.

** 3. Is Chapter 11 of Class 12 Maths, ‘3D Geometry and Vector’ to grasp?**

Although Chapter 11 of Class 12 Maths, ‘3D Geometry and Vector,’ is not tough, it can be confusing due to the many topics and equations listed in the chapter. However, once students are comfortable with problems relevant to the ideas taught, the chapter is quite simple to master. Students are encouraged to use Chapter 11 revision notes because these brief notes can help them quickly cover a lot of ground. Also, if a student maintains a formula notebook for this chapter, they will have no difficulty remembering the formulas and theory.

** 4. In CBSE term 2 Maths, what is the purpose of a formula notebook?**

A formula notebook is a separate notebook used by students to keep track of significant formulas and theories. The formula notebook only contains the most important information. Students use this notebook to keep essential notes for the examination. This notebook comes in handy for last-minute revision. It is a fact that a student forgets a crucial formula while solving mock tests and sample papers due to exam pressure. They can look for it in their notebook rather than sifting through hundreds of reference book pages.

** 5. Is NCERT enough for scoring good marks in 3D geometry and Vectors?**

No! The NCERT books provide a student with an overview of the entire chapter in a common person’s language. There are a lot of exercises to practise from the NCERT, but they are not sufficient. You might say that the CBSE Maths question paper is based on the syllabus of the NCERT books. NCERT, on the other hand, is insufficient to achieve above-average results. You may need the help of reference books such as R.D.ShaR.D. Sharma’sgarwaAggarwal’sthers to grasp specific subjects. The RD Sharma Solutions and RS Aggarwal Solutions train students not just for CBSE class 12 but also for the JEE Main 2022 and JEE Advanced 2022 Exams.

** 6. How should a student attempt the questions of 3D geometry and vectors?**

Students will be taking offline subjective tests this term; therefore, breaking problems of ‘3D geometry and vectors’ steps can assist students in receiving better results. Step marking is beneficial if the student knows partially about the solution, resulting in some marks. For example, suppose you complete a four-mark question and compute the incorrect answer by accident. You will be granted marks in such circumstances until the procedure is accurate. No marks will be provided once the technique is incorrect. The stepwise answer approach also helps you analyse the problem.