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

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Questions
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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