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NCERT Solutions for class 12 Maths | Chapter 11 - Three Dimensional Geometry

(1) The coordinates of the midpoints of the line segment joining the points (2, 3, 4) and (8, -3, 8) are
[A] (10, 0, 12)
[B] (5, 6, 0)
[C] (6, 5, 0)
[D] (5, 0, 6)
Answer: (5, 0, 6)t
(2) The direction cosines of the y-axis are
[A] (6, 0, 0)
[B] (1, 0, 0)
[C] (0, 1, 0)
[D] (0, 0, 1)
Answer: (0, 1, 0)

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(3) The direction ratios of a line are 1,3,5 then its direction cosines are
[A] 1/√35, 3/√35, 5/√35
[B] 1/9, 1/3, 5/9
[C] 5/√35, 3/√35, 1/√35
[D] None of these
Answer: 1/√35, 3/√35, 5/√35
(4) The points A (1, 1, 0), B(0, 1, 1), C(1, 0, 1) and D(2/3, 2/3, 2/3)
[A] Coplanar
[B] Non-coplanar
[C] Vertices of a parallelogram
[D] None of these
Answer: Coplanar
(5) The distance of the plane from the orgin is
[A] 1
[B] 7
[C] 1/7
[D] None of these
Answer: 1
(6) The cosines of the angle between any two diagonals of a cube is
[A] 1/3
[B] 1/2
[C] 2/3
[D] 1√3
Answer: 1/3
(7) The planes and
[A] parallel
[B] at right angles
[C] equidistant front origin
[D] None of these
Answer: parallel
(8) The sine of the angle between the straight line and the plane 2x – 2y + z = 5 is
[A]
[B]
[C]
[D]
Answer:
(9) The plane 2x – 3y + 6z – 11 = 0 makes an angle sin-1 (α) with .e-axis. The value of a is equal to
[A] √3/2
[B] √2/3
[C] 2/7
[D] 3/7
Answer: 2/7
(10) The distance of the points (2, 1, -1) from the plane x- 2y + 4z – 9 is
[A] √31/21
[B] 13/21
[C] 13/√21
[D] √π/2
Answer: 13/21
(11) The direction cosines of the line joining (1, -1, 1) and (-1, 1, 1) are
[A] 2, -2, 0
[B] 1, -1, 0
[C] 1/√2, – 1/√2
[D] None of these
Answer: 1/√2, – 1/√2
(12) The length of the ⊥er from the point (0, – 1, 3) to the plane 2x + y – 2z + 1 = 0 is
[A] 0
[B] 2√3
[C] 2/3
[D] 2
Answer: 2
(13) If the directions cosines of a line are A, k, k, then
[A] k > 0
[B] 0 < k < 1
[C] k = 1
[D]
Answer:
(14) Distance of the point (a, β, γ) from y-axis is
[A] β
[B] |β|
[C] 60 J
[D]
Answer:
(15) If the planes a1x + b, y + c, z + d1 = 0 and a2x + b, y + c2z + d2 = 0 are perpendicular to each other then
[A]
[B]
[C] a1a2 + b1b2 + c1c2 = 0
[D]
Answer: a1a2 + b1b2 + c1c2 = 0
(16) The direction ratios of the line joining the points (x, y, z) and (x2, y2, z1) are
[A] x1 + x2, y1 + y2, z1 + z2
[B]
[C]
[D] x2 – x1, y2 – y1, z2 – z1
Answer: x2 – x1, y2 – y1, z2 – z1
(17) The direction cosines of the normal to the plane 2x – 3y – 6z – 3 = 0 are
[A] 2/7, −3/7, −6/7
[B] 2/7, 3/7, 6/7
[C] −2/7, −3/7, −6/7
[D] None of these
Answer: 2/7, −3/7, −6/7
(18) The shortest distance between the lines
[A] 0
[B]
[C]
[D]
Answer: 0
(19) The lines of intersection of the planes is parallel to the vector
[A]
[B]
[C]
[D]
Answer:
(20) The angle between the planes 2x – y + z = 6 and x + y + 2z = 7 is
[A] π/4
[B] π/6
[C] π/3
[D] π/2
Answer: π/3

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