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

(1) The distance of point P(3,4, 5) from the yz-plane is
[A] 3 units
[B] 4 units
[C] 5 units
[D] 550
Answer: 3 units
(2) Under what condition does the equation x2 + y2 + z2 + 2ux + 2vy + 2wz + d represent a real sphere
[A] u2 + v2 + w2 = d2
[B] u2 + v2 + w2 > d
[C] u2 + v2 + w2 < d
[D] u2 + v2 + w2 < d2
Answer: u2 + v2 + w2 > d

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(3) The coordinate of foot of perpendicular drawn from the point A(1, 0, 3) to the join of the point B(4, 7, 1) and C(3, 5, 3) are
[A] (5/3, 7/3, 17/3)
[B] (5, 7, 17)
[C] (5/3, -7/3, 17/3)
[D] (5/7, -7/3, -17/3)
Answer: (5/3, 7/3, 17/3)
(4) Three planes x + y = 0 , y + z = 0 , and x + z = 0
[A] none of these
[B] meet in a line
[C] meet in a unique point
[D] meet taken two at a time in parallel lines
Answer: meet in a unique point
(5) The locus of a point which moves so that the difference of the squares of its distances from two given points is constant, is a
[A] Straight line
[B] Plane
[C] Sphere
[D] None of these
Answer: Plane
(6) The coordinates of the point where the line through (5, 1, 6) and (3, 4, 1) crosses the YZ plane is
[A] (0, 17/2, 13/2)
[B] (0, -17/2, -13/2)
[C] (0, 17/2, -13/2)
[D] None of these
Answer: (0, 17/2, -13/2)
(7) The ratio in which the line joining the points(1,2,3) and (-3,4,-5) is divided by the xy-plane is
[A] 2 : 5
[B] 3 : 5
[C] 5 : 2
[D] 5 :3
Answer: 3 : 5
(8) The dirction cosines of a line equally inclined to three mutually perpendicular lines having DCs as l1 ,m1 , n1 ,  l2 ,m2 , n2 , l3 ,m3 , n3 are
[A] l1 + l2 , l3 ,  m1 + m2 + m3 , n1 + n2 + n3
[B] (l1 + l2 , l3 )/3,  (m1 + m2 + m3 )/3 , (n1 + n2 + n)/3
[C] (l1 + l2 , l3 )/√3,  (m1 + m2 + m3 )/√3 , (n1 + n2 + n)/√3
[D] None of these
Answer: (l1 + l2 , l3 )/√3,  (m1 + m2 + m3 )/√3 , (n1 + n2 + n)/√3
(9) The points A(3, 3, 3), B(0, 6, 3), C(1, 7, 7) and D(4, 4, 7) are the vertices of a
[A] Rectangle
[B] Square
[C] Rhombus
[D] None of these
Answer: Square
(10) The equation of plane containing the line of intersection of the plane x + y + z - 6 = 0 and 2x + 3y + 4z + 5 = 0 and passing through the point (1, 1, 1) is
[A] 20x + 23y + 26z + 69 = 0
[B] 20x + 23y - 26z - 69 = 0
[C] 20x - 23y + 26z - 69 = 0
[D] 20x + 23y + 26z - 69 = 0
Answer: 20x + 23y + 26z - 69 = 0
(11) There is one and only one sphere through
[A] 4 points not in the same plane
[B] 4 points not lie in the same straight line
[C] none of these
[D] 3 points not lie in the same line
Answer: 4 points not in the same plane
(12) If the equation of a plane is lx + my + nz = p is in the normal form, then which is not true
[A] l, m and n are the direction cosines of the normal to the plane
[B] p is the length of the perpendicular from the origin to the plane
[C] The plane passes through the origin for all values of p
[D] l2 + m2 + n2 = 1
Answer: The plane passes through the origin for all values of p
(13) The angle between the planes r . n1 = d1 and r . n2 = d2 is
[A] cos θ ={|n1 | * |n2 |}/ (n1 . n2 )
[B] cos θ = (n1 . n2 )/{|n1 | * |n2 |}2
[C] cos θ = (n1 . n2 )/{|n1 | * |n2 |}
[D] cos θ = (n1 . n2 )2 /{|n1 | * |n2 |}
Answer: cos θ = (n1 . n2 )/{|n1 | * |n2 |}
(14) The centroid of ∆ ABC is at (1, 1, 1). If coordinates of A and B are (3, -5, 7) and (-1, 7, -6) respectively then the coordinates of point C is
[A] (1, -1, 2)
[B] (1, 1, -2)
[C] (1, 1, 2)
[D] (-1, 1, 2)
Answer: (1, 1, 2)
(15) If the points A(1, 0, –6), B(–5, 9, 6) and C(–3, p, q) are collinear, then the value of p and q are
[A] -6 and -2
[B] -6 and 2
[C] 6 and -2
[D] 6 and 2
Answer: 6 and 2
(16) The image of the point P(1,3,4) in the plane 2x - y + z = 0 is
[A] (-3, 5, 2)
[B] (3, 5, 2)
[C] (3, -5, 2)
[D] (3, 5, -2)
Answer: (-3, 5, 2)
(17) The projections of a directed line segment on the coordinate axes are 12, 4, 3. The DCS of the line are
[A] 12/13, -4/13, 3/13
[B] -12/13, -4/13, 3/13
[C] 12/13, 4/13, 3/13
[D] None of these
Answer: 12/13, 4/13, 3/13
(18) The equation of plane passing through the point i + j + k and parallel to the plane r . (2i - j + 2k) = 5 is
[A] r . (2i - j + 2k) = 2
[B] r . (2i - j + 2k) = 3
[C] r . (2i - j + 2k) = 4
[D] r . (2i - j + 2k) = 5
Answer: r . (2i - j + 2k) = 3
(19) The vector equation of a sphere having centre at origin and radius 5 is
[A] |r| = 5
[B] |r| = 25
[C] |r| = √5
[D] none of these
Answer: |r| = 5
(20) A parallelepiped is formed by planes drawn through the points (2,3,5) and (5,9,7), parallel to the coordinate plane. The length of a diagonal of the parallelopiped is
[A] 7
[B] √38
[C] √155
[D] none of these
Answer: 7

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