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Three Dimensional Geometry · Question 24

JEE Main 2026 (Online) 23rd January Morning ShiftMCQMedium📈 Topic in 10% papers+4−1
1

Let the direction cosines of two lines satisfy the equations : 4l + m - n = 0 and 2mn + 10nl + 3lm = 0. Then the cosine of the acute angle between these lines is :

  1. 107 38
  2. 10 38
  3. 103 38
  4. 203 38

Answer

(3) 103 38

Solution

From the first equation: n = 4l + m

Substitute in the second: 2m(4l + m) + 10l(4l + m) + 3lm = 0

40l2 + 21lm + 2m2 = 0

(8l + m)(5l + 2m) = 0

Case 1: m = -8l n = -4l d.r. (1, -8, -4), magnitude = 9

Case 2: m = - 5l2 n = 3l2 d.r. (2, -5, 3), magnitude = 38

= |(1)(2) + (-8)(-5) + (-4)(3)|9 38

= 309 38 = 103 38

Answer: (3)

JEE Main 2026 (Online) 23rd January Morning Shift

Keep practising — Three Dimensional Geometry

2

The vertices B and C of a triangle ABC lie on the line x1 = 1 - y-2 = z - 23. The coordinates of A and B are (1, 6, 3) and (4, 9, α) respectively and C is at a distance of 10 units from B. The area (in sq. units) of ABC is :

  1. 20 13
  2. 5 13
  3. 15 13
  4. 10 13
JEE Main 2026 (Online) 23rd January Morning Shift
3

If the image of the point P(a, 2, a) in the line x2 = y + a1 = z1 is Q and the image of Q in the line x - 2b2 = y - a1 = z + 2b-5 is P , then a + b is equal to .

JEE Main 2026 (Online) 23rd January Evening Shift
4

Let P( , , ) be the point on the line x - 12 = y + 1-3 = z at a distance 4 14 from the point (1, -1, 0) and nearer to the origin. Then the shortest distance, between the lines x - 1 = y - 2 = z - 3 and x + 52 = y - 101 = z - 31, is equal to

  1. 4 75
  2. 7 54
  3. 4 57
  4. 2 74
JEE Main 2026 (Online) 22nd January Morning Shift
5

If the image of the point P(1, 2, a) in the line x - 63 = y - 72 = 7 - z2 is Q(5, b, c), then a2 + b2 + c2 is equal to

  1. 298
  2. 264
  3. 293
  4. 283
JEE Main 2026 (Online) 22nd January Morning Shift
6

Let L be the line x+12 = y+13 = z+36 and let S be the set of all points (a, b, c) on L, whose distance from the line x+12 = y+13 = z-90 along the line L is 7. Then (a, b, c) S (a + b + c) is equal to :

  1. 28
  2. 6
  3. 40
  4. 34
JEE Main 2026 (Online) 22nd January Evening Shift
7

Let ( , , ) be the co-ordinates of the foot of the perpendicular drawn from the point (5, 4, 2) on the line r = (- i + 3 j + k) + (2 i + 3 j - k). Then the length of the projection of the vector i + j + k on the vector 6 i + 2 j + 3 k is :

  1. 187
  2. 157
  3. 4
  4. 3
JEE Main 2026 (Online) 21st January Morning Shift
8

Let the line L pass through the point (-3, 5, 2) and make equal angles with the positive coordinate axes. If the distance of L from the point (-2, r, 1) is 143, then the sum of all possible values of r is :

  1. 16
  2. 12
  3. 6
  4. 10
JEE Main 2026 (Online) 21st January Evening Shift
9

Let the line L1 be parallel to the vector -3 i + 2 j + 4 k and pass through the point (2, 6, 7), and the line L2 be parallel to the vector 2 i + j + 3 k and pass through the point (4, 3, 5). If the line L3 is parallel to the vector -3 i + 5 j + 16 k and intersects the lines L1 and L2 at the points C and D, respectively, then | CD |2 is equal to:

  1. 290
  2. 171
  3. 89
  4. 312
JEE Main 2026 (Online) 21st January Evening Shift
10

Let the values of for which the shortest distance between the lines x-12 = y-23 = z-34 and x- 3 = y-44 = z-55 is 1 6 be 1 and 2. Then the radius of the circle passing through the points (0, 0), ( 1, 2) and ( 2, 1) is

  1. 3
  2. 5 23
  3. 23
  4. 4
JEE Main 2025 (Online) 8th April Evening Shift
11

Let the area of the triangle formed by the lines x + 2 = y - 1 = z, x - 35 = y-1 = z - 11 and x-3 = y - 33 = z - 21 be A. Then A2 is equal to .

JEE Main 2025 (Online) 8th April Evening Shift

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