Maths NCERT Exemplar Solutions Class 12th Chapter Eleven: Overview, Questions, Preparation

Maths NCERT Exemplar Solutions Class 12th Chapter Eleven 2025 ( Maths NCERT Exemplar Solutions Class 12th Chapter Eleven )

Payal Gupta
Updated on Jul 15, 2025 10:48 IST

By Payal Gupta, Retainer

Table of content
  • Three-Dimensional Geometry Long Answer Type Questions
  • Three-Dimensional Geometry Short Answer Type Questions
  • Three-Dimensional Geometry Objective Type Questions
  • Three-Dimensional Geometry Fill in the blanks Type Questions
  • Three-Dimensional Geometry True or False Type Questions
Maths NCERT Exemplar Solutions Class 12th Chapter Eleven Logo

Three-Dimensional Geometry Long Answer Type Questions

1. Find the foot of the perpendicular from the point (2, 3, –8) to the line 4 x 2 = y 6 = 1 z 3 . Also, find the perpendicular distance from the given point to the line.

Ans. G i v e n t h a t 4 x 2 + y 6 + 1 z 3 i s t h e e q u a t i o n o f l i n e x 4 2 + y 6 + z 1 3 = λ C o o r d i n a t e s o f a n y point Q o n t h e l i n e a r e x = 2 λ + 4 , y = 6 λ a n d z = 3 λ + 1 a n d t h e g i v e n point i s P ( 2 , 3 , 8 ) D i r e c t i o n r a t i o s o f P Q a r e 2 λ + 4 2 , 6 λ 3 , 3 λ + 1 + 8 a n d t h e D ' r a t i o s o f t h e g i v e n l i n e a r e 2 , 6 , 3 . I f P Q l i n e t h e n 2 ( 2 λ + 2 ) + 6 ( 6 λ 3 ) 3 ( 3 λ + 9 ) = 0 4 λ 4 + 3 6 λ 1 8 + 9 λ 2 7 = 0 4 9 λ 4 9 = 0 λ = 1 T h e f o o t o f t h e p e r p e n d i c u l a r i s 2 ( 1 ) + 4 , 6 ( 1 ) , 3 ( 1 ) + 1 i . e . , 2 , 6 , 2 N o w , distance P Q = ( 2 2 ) 2 + ( 3 6 ) 2 + ( 8 + 2 ) 2 = 9 + 3 6 = 4 5 = 3 5 H e n c e , t h e r e q u i r e d c o o r d i n a t e s o f t h e f o o t o f t h e p e r p e n d i c u l a r a r e 2 , 6 , 2 a n d t h e r e q u i r e d distance 3 5 u n i t s .

2. Find the distance of the point (2, 4, –1) from the line x + 5 1 = y + 3 4 = z 6 9 .

Ans. T h e g i v e n e q u a t i o n o f l i n e i s x + 5 1 = y + 3 4 = z 6 9 = λ a n d a n y point P ( 2 , 4 , 1 ) L e t Q b e a n y point o n t h e g i v e n l i n e C o o r d i n a t e s o f Q a r e x = λ 5 , y = 4 λ 3 a n d z = 9 λ + 6 a n d t h e g i v e n point i s P ( 2 , 3 , 8 ) D i r e c t i o n r a t i o s o f P Q a r e λ 5 2 , 4 λ 3 4 , 9 λ + 6 + 1 i . e . , λ 7 , 4 λ 7 , 9 λ + 7 a n d t h e D ' r a t i o s o f t h e g i v e n l i n e a r e 1 , 4 , 9 . I f P Q l i n e t h e n 1 ( λ 7 ) + 4 ( 4 λ 7 ) 9 ( 9 λ + 7 ) = 0 λ 7 + 1 6 λ 2 8 + 8 1 λ 6 3 = 0 9 8 λ 9 8 = 0 λ = 1 S o , C o o r d i n a t e s o f Q a r e 1 5 , 4 × 1 3 , 9 × 1 + 6 i . e . , 4 , 1 , 3 N o w , distance P Q = ( 4 2 ) 2 + ( 1 4 ) 2 + ( 3 + 1 ) 2 = ( 6 ) 2 + ( 3 ) 2 + ( 2 ) 2 = 3 6 + 9 + 4 = 4 9 = 7 H e n c e , t h e r e q u i r e d distance 7 u n i t s .
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Commonly asked questions
Q:  

Find the foot of the perpendicular from the point (2, 3, –8) to the line 4 x 2 = y 6 = 1 z 3 . Also, find the perpendicular distance from the given point to the line.

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Q:  

Find the distance of the point (2, 4, –1) from the line x + 5 1 = y + 3 4 = z 6 9 .

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Q:  

Find the length and the foot of the perpendicular from the point ( 1 , 3 2 , 2 ) to the plane 2 x 2 y + 4 z + 5 = 0 .

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Maths NCERT Exemplar Solutions Class 12th Chapter Eleven Logo

Three-Dimensional Geometry Short Answer Type Questions

1. Find the position vector of a point A in space such that O A is inclined at 60º to OX and at 45° to OY and | O A | = 10 units.
Ans. L e t α = 6 0 0 , β = 4 5 0 a n d t h e a n g l e i n c l i n e d t o O Z a x i s b e γ . W e k n o w t h a t c o s 2 α + c o s 2 β + c o s 2 γ = 1 c o s 2 6 0 0 + c o s 2 4 5 0 + c o s 2 γ = 1 ( 1 2 ) 2 + ( 1 2 ) 2 + c o s 2 γ = 1 1 4 + 1 2 + c o s 2 γ = 1 3 4 + c o s 2 γ = 1 c o s 2 γ = 1 3 4 = 1 4 c o s γ = ± 1 2 c o s γ = 1 2 ( Rejecting c o s γ = 1 2 , since γ < 9 0 0 ) O A = | O A | ( 1 2 i ^ + 1 2 j ^ + 1 2 k ^ ) = 1 0 ( 1 2 i ^ + 1 2 j ^ + 1 2 k ^ ) = 5 i ^ + 5 2 j ^ + 5 k ^ H e n c e , t h e p o s i t i o n v e c t o r o f A i s ( 5 i ^ + 5 2 j ^ + 5 k ^ ) .
2. Find the vector equation of the line which is parallel to the vector 3 i ^ 2 j ^ + 6 k ^ and which passes through the point (1, –2, 3).
Ans. W e k n o w t h a t t h e e q u a t i o n o f l i n e i s r = a + b λ H e r e , a = i ^ 2 j ^ + 3 k ^ a n d b = 3 i ^ 2 j ^ + 6 k ^ E q u a t i o n o f l i n e i s r = ( i ^ 2 j ^ + 3 k ^ ) + λ ( 3 i ^ 2 j ^ + 6 k ^ ) ( x i ^ + y j ^ + z k ^ ) = ( i ^ 2 j ^ + 3 k ^ ) + λ ( 3 i ^ 2 j ^ + 6 k ^ ) ( x i ^ + y j ^ + z k ^ ) ( i ^ 2 j ^ + 3 k ^ ) = λ ( 3 i ^ 2 j ^ + 6 k ^ ) ( x 1 ) i ^ + ( y + 2 ) j ^ + ( z 3 ) k ^ = λ ( 3 i ^ 2 j ^ + 6 k ^ ) H e n c e , t h e r e q u i r e d e q u a t i o n i s ( x 1 ) i ^ + ( y + 2 ) j ^ + ( z 3 ) k ^ = λ ( 3 i ^ 2 j ^ + 6 k ^ ) .
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Commonly asked questions
Q:  

Find the position vector of a point A in space such that O A is inclined at 60º to OX and at 45° to OY and | O A | = 10 units.

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Q:  

Show that the lines x 1 2 = y 2 3 = z 3 4   and x 4 5 = y 1 2 = z   intersect. Also, find their point of intersection.

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Q:  

Find the vector equation of the line which is parallel to the vector 3 i ^ 2 j ^ + 6 k ^ and which passes through the point (1, –2, 3).

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Maths NCERT Exemplar Solutions Class 12th Chapter Eleven Logo

Three-Dimensional Geometry Objective Type Questions

1. The distance of the point ( α , β , γ ) from the y-axis is

(A) β

(B) γ

(C) β 2 + γ 2

(D) α 2 + γ 2

 Ans. T h e g i v e n point i s ( α , β , γ ) A n y point o n y a x i s = ( 0 , β , 0 ) Required distance = ( α 0 ) 2 + ( β β ) 2 + ( δ 0 ) 2 = α 2 + γ 2 H e n c e , t h e c o r r e c t o p t i o n i s ( d ) .

2. If the direction cosines of a line are k , k , k , then:

(A) k > 0

(B) 0 < k < 1

(C) k = 1

(D) k = 1 3 or - 1 3

Ans. I f l , m , n a r e t h e d i r e c t i o n c o s i n e s o f a l i n e , t h e n l 2 + m 2 + n 2 = 1 S o , k 2 + k 2 + k 2 = 1 3 k 2 = 1 k = ± 1 3 H e n c e , t h e c o r r e c t o p t i o n i s ( d ) .
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Commonly asked questions
Q:  

The distance of the point ( α , β , γ ) from the y-axis is

(A) β

(B) γ

(C) β 2 + γ 2

(D) α 2 + γ 2

Q:  

If the direction cosines of a line are k , k , k , then:

(A) k > 0

(B) 0 < k < 1

(C) k = 1

(D) k = 1 3 or - 1 3

Q:  

The distance of the plane  from the origin is:

(A) 1

(B) 7

(C) 1 7

(D) None of these

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Maths NCERT Exemplar Solutions Class 12th Chapter Eleven Logo

Three-Dimensional Geometry Fill in the blanks Type Questions

1. A plane passes through the points (2, 0, 0), (0, 3, 0), and (0, 0, 4). The equation of the plane is __________.

Ans. G i v e n points a r e ( 2 , 0 , 0 ) , ( 0 , 3 , 0 ) a n d ( 0 , 0 , 4 ) . S o , t h e intercepts c u t s b y t h e p l a n e o n t h e a x e s a r e 2 , 3 , 4 E q u a t i o n o f t h e p l a n e ( intercept f o r m ) i s x a + y b + z c = 1 x 2 + y 3 + z 4 = 1 H e n c e , t h e e q u a t i o n o f t h e p l a n e i s x 2 + y 3 + z 4 = 1
2. The direction cosines of the vector ( 2 i ^ + 2 j ^ k ^ ) are __________.
Ans. L e t a = 2 i ^ + 2 j ^ k ^ d i r e c t i o n r a t i o s o f a a r e 2 , 2 , 1 t h e d i r e c t i o n cosines a r e 2 4 + 4 + 1 , 2 4 + 4 + 1 , 1 4 + 4 + 1 2 3 , 2 3 , 1 3 H e n c e , t h e d i r e c t i o n cosines o f t h e g i v e n v e c t o r a r e 2 3 , 2 3 , 1 3 .
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Commonly asked questions
Q:  

A plane passes through the points (2, 0, 0), (0, 3, 0), and (0, 0, 4). The equation of the plane is __________.

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Q:  

The direction cosines of the vector ( 2 i ^ + 2 j ^ k ^ ) are __________.

Q:  

The vector equation of the line x 5 3 = y + 4 7 = z 6 2   is __________.

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Maths NCERT Exemplar Solutions Class 12th Chapter Eleven Logo

Three-Dimensional Geometry True or False Type Questions

1. The unit vector normal to the plane x + 2 y + 3 z 6 = 0  is 1 / 1 4 i ^ + 2 / 1 4 j ^ + 3 / 1 4 k ^ .
Ans. G i v e n p l a n e i s x + 2 y + 3 z 6 = 0 V e c t o r n o r m a l t o t h e p l a n e n = i ^ + 2 j ^ + 3 k ^ n ^ = n | n | = i ^ + 2 j ^ + 3 k ^ ( 1 ) 2 + ( 2 ) 2 + ( 3 ) 2 = 1 1 4 i ^ + 2 1 4 j ^ + 3 1 4 k ^ H e n c e , t h e g i v e n s t a t e m e n t i s T r u e .
2. The intercepts made by the plane 2 x 3 y + 5 z + 4 = 0 on the coordinate axis are 2 , 4 3 , 4 5 .
Ans. E q u a t i o n o f t h e p l a n e i s 2 x 3 y + 5 z + 4 = 0 2 x 3 y + 5 z = 4 2 4 x 3 4 y + 5 4 z = 1 x 2 y 4 / 3 + z 4 / 5 = 1 S o , t h e r e q u i r e d intercepts a r e 2 , 4 3 a n d 4 5 H e n c e , t h e g i v e n s t a t e m e n t i s T r u e .
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Commonly asked questions
Q:  

The unit vector normal to the plane x + 2 y + 3 z 6 = 0 is 1 / 1 4 i ^ + 2 / 1 4 j ^ + 3 / 1 4 k ^ .

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Q:  

The intercepts made by the plane 2 x 3 y + 5 z + 4 = 0 on the coordinate axis are 2 , 4 3 , 4 5 .

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Q:  

The angle between the line   r   = ( 5 i ^ + 3 j ^ + 7 k ^ )   + λ ( 2 i ^ j ^ + k ^ )   and the plane r = 3 i ^ 4 j ^ 4 k ^   + 5 = 0 is s i n 1 ( 5 / 2 9 1 ) .             .

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Maths NCERT Exemplar Solutions Class 12th Chapter Eleven Exam

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