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Three Dimensional Geometry · Question 26

JEE Main 2026 (Online) 23rd January Evening ShiftNumericalMedium📈 Topic in 68% papers+4
1

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 .

Answer

3

Solution

Q is the image of P in L1 and P is the image of Q in L2, so the midpoint M of PQ lies on both lines and PQ L1, PQ L2.

M is the point of intersection of L1 and L2.

L1: (2s, s - a, s); L2: (2b + 2u, a + u, -2b - 5u)

Equating: 2s = 2b + 2u, s - a = a + u, s = -2b - 5u

s = b + u = 2a + u b = 2a

b + u = -2b - 5u u = - b2, s = b2 = a

M = (2a, 0, a)

MP = (a - 2a, 2 - 0, a - a) = (-a, 2, 0) must be to L1 (d.r. 2, 1, 1):

-2a + 2 + 0 = 0 a = 1

Check with L2 (d.r. 2, 1, −5): -2 + 2 + 0 = 0 ✓

b = 2a = 2

a + b = 1 + 2 = 3

Answer: 3

JEE Main 2026 (Online) 23rd January Evening Shift

Keep practising — Three Dimensional Geometry

2

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

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  3. 4 57
  4. 2 74
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3

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4

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 :

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  2. 6
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6

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
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JEE Main 2026 (Online) 21st January Evening Shift
7

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:

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8

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
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9

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 .

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Let the line L pass through (1, 1, 1) and intersect the lines x-12 = y+13 = z-14 and x-31 = y-42 = z1. Then, which of the following points lies on the line L?

  1. (7, 15, 13)
  2. (4, 22, 7)
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11

If the shortest distance between the lines x-12 = y-23 = z-34 and x1 = y = z-51 is 5 6, then the sum of all possible values of is

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JEE Main 2025 (Online) 7th April Morning Shift

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