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3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - JEE MCQ


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10 Questions MCQ Test - 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec)

3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) for JEE 2024 is part of JEE preparation. The 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) questions and answers have been prepared according to the JEE exam syllabus.The 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) MCQs are made for JEE 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) below.
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3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 1

The direction cosines l, m and n of two lines are connected by the relations l + m + n = 0 and lm = 0, then the angle between the lines is

Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 1

Given, ...(i)
and
i.e. either or
If , then putting in equation (i), we get
∴ Direction ratios are i.e.
If , then putting in equation (i), we get
∴ Direction ratios are i.e.

3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 2

A line makes with positive -axis and makes equal angles with positive axes, respectively. What is the sum of the three angles which the line makes with positive and axes?

Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 2
We know that sum of square of direction cosines i.e.

(As given and )


, Negative value is discarded,
Since the line makes angle with positive axes. Hence,


Required sum
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3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 3

What are the direction cosines of a line which is equally inclined to the positive directions of the axes?

Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 3

Let ℓ,m,n are the dc's of a line that is inclined equally at α to the + ve direction of axes. Now, ℓ = cosα, m = cosα, n = cosα
Also, ℓ+ m+ n2 = 1

∴ dc's of the line are : 

3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 4
A line makes the same angle with each of the and axes. If the angle , which it makes with the -axis, is such that , then what is the value of ?
Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 4
Since

line makes the same angle with and -axes and with z-axis) Also,

.......(2)
- From equation (i) and (ii)
3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 5

If a line makes angle and with the -axis and -axis respectively, then the angle made by the line with the -axis is

Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 5

We know that,
cos2α + cos2β + cos2γ = 1
∴ 

3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 6

The direction cosines of two lines are related by l + m + n = 0 and al+ bm+ cn= 0. The lines are parallel if

Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 6

For n = −(l + m), the second relation gives or

For parallel lines, the two roots must be equal
Dividing by will get final answer.

3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 7
A line makes angles and with axes respectively. Consider the following
1.
2.
3.
Which of the above is/are correct?
Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 7
If a line makes angle and with axes respectively, then


Statement (2) is correct.
3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 8
Consider the following relations among the angles and made by a vector with the coordinate axes
1.
II.
Which of the above is/are correct?
Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 8
We have,
...(i)


Hence statement - I is correct. and now from (i),

Hence, only statement I is correct.
3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 9
If the direction cosines of a line are then
Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 9
Since d. c. of line are
3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 10
If a line makes angles with the positive directions of and -axes respectively, then the value of
Detailed Solution for 3-D Geometry: Direction Ratios and Direction Cosines(13 Dec) - Question 10
Direction cosines will be
So,
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