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 Page 1


Edurev123 
8. Hyperboloid of One and Two Sheets and 
its Properties 
8.1 Find the vertices of the skew quadrilateral formed by the four generators of the 
hyperboloid 
?? ?? ?? +?? ?? -?? ?? =???? 
passing through (???? ,?? ,?? ) and (???? ,?? ,-?? ) . 
(2010 : 20 Marks) 
Solution: 
Given, the equation of hyperboloid is 
?? 2
4
+?? 2
-?? 2
=49 
It can be rewritten as 
(
?? 2
-?? )(
?? 2
+?? )=(7-?? )(7+?? ) 
? The equation of two systems of generating lines are : 
(
?? 2
-?? )=?? (7-?? ),?? (
?? 2
+?? )=(7+?? ) (1)
(
?? 2
-?? )=?? (7+?? ),?? (
?? 2
+?? )=(7-?? ) (2)
 
(1) and (2) pass through (10,5,1) and (14,2,-2) for ?? =2,?? =
1
3
 and ?? =
9
5
,?? =1. 
So, the two systems of generating lines are 
(
?? 2
-?? )=2(7-?? ), (
?? 2
+?? )=7+?? (3)
(
?? 2
-?? )=
1
3
(7+?? ),
1
3
(
?? 2
+?? )=7-?? (4)
(
?? 2
-?? )=
9
5
(7-?? ),
9
5
(
?? 2
+2)=7+?? (5)
(
?? 2
-?? )=1(7+?? ),
?? 2
+?? =7-?? (6)
 
Solving (3) and (6), we get the vertices as (14,
7
3
,-
7
3
) . 
Page 2


Edurev123 
8. Hyperboloid of One and Two Sheets and 
its Properties 
8.1 Find the vertices of the skew quadrilateral formed by the four generators of the 
hyperboloid 
?? ?? ?? +?? ?? -?? ?? =???? 
passing through (???? ,?? ,?? ) and (???? ,?? ,-?? ) . 
(2010 : 20 Marks) 
Solution: 
Given, the equation of hyperboloid is 
?? 2
4
+?? 2
-?? 2
=49 
It can be rewritten as 
(
?? 2
-?? )(
?? 2
+?? )=(7-?? )(7+?? ) 
? The equation of two systems of generating lines are : 
(
?? 2
-?? )=?? (7-?? ),?? (
?? 2
+?? )=(7+?? ) (1)
(
?? 2
-?? )=?? (7+?? ),?? (
?? 2
+?? )=(7-?? ) (2)
 
(1) and (2) pass through (10,5,1) and (14,2,-2) for ?? =2,?? =
1
3
 and ?? =
9
5
,?? =1. 
So, the two systems of generating lines are 
(
?? 2
-?? )=2(7-?? ), (
?? 2
+?? )=7+?? (3)
(
?? 2
-?? )=
1
3
(7+?? ),
1
3
(
?? 2
+?? )=7-?? (4)
(
?? 2
-?? )=
9
5
(7-?? ),
9
5
(
?? 2
+2)=7+?? (5)
(
?? 2
-?? )=1(7+?? ),
?? 2
+?? =7-?? (6)
 
Solving (3) and (6), we get the vertices as (14,
7
3
,-
7
3
) . 
Solving (4) and (5), we get the vertices as (
21
2
,
77
16
,
21
16
) . 
? Other two vertices are (14,
7
3
,-
7
3
) and (
21
2
,
77
16
,
21
16
) . 
8.2 Show that the generators through any one of the ends of an equiconjugate 
diameter of the principal elliptic section of the hyperboloid 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? are 
inclined to each other at an angle of ????
°
 if ?? ?? +?? ?? =?? ?? ?? . Find also the condition 
for the generators to be perpendicular to each other. 
(2011 : 20 Marks) 
Solution: 
Let ( ?? cos ?? ,?? sin ?? ,0 ) be the given point on the diameter. 
The equations of the two generators through this point are 
?? -?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±?? 
The direction ratios of two generators are (?? sin ?? ,-?? cos ?? ,?? ) and (?? sin ?? ,-?? cos ?? ,-?? ) 
respectively. 
Let ?? be the angle between two generators and let ?? be the parameter of the end points 
of conjugate diameters. 
 cos ?? =
?? 1
?? 2
+?? 1
?? 2
+?? 1
?? 2
v?? 1
2
:?? 1
2
+?? 1
2
v?? 2
2
+?? 2
2
+?? 2
2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 
Putting ?? =60
°
 and ?? =45
°
 ( ? equi-conjugal diameters means equal length of conjugal 
diameters, l.e., v?? 2
cos
2
 ?? +?? 2
sin
2
 ?? which is equal to v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? and is 
possible for ?? =45
°
 ). 
? from (i), we get 
                                 cos 60
°
=
?? 2
2
+
?? 2
2
-?? 2
?? 2
2
+
?? 2
2
+?? 2
 ?                                      
1
2
=
?? 2
+?? 2
-2?? 2
?? 2
+?? 2
+2?? 2
 ?              ?? 2
+?? 2
+2?? 2
=2?? 2
+2?? 2
-4?? 2
 ?                          ?? 2
+?? 2
=6?? 2
 
Page 3


Edurev123 
8. Hyperboloid of One and Two Sheets and 
its Properties 
8.1 Find the vertices of the skew quadrilateral formed by the four generators of the 
hyperboloid 
?? ?? ?? +?? ?? -?? ?? =???? 
passing through (???? ,?? ,?? ) and (???? ,?? ,-?? ) . 
(2010 : 20 Marks) 
Solution: 
Given, the equation of hyperboloid is 
?? 2
4
+?? 2
-?? 2
=49 
It can be rewritten as 
(
?? 2
-?? )(
?? 2
+?? )=(7-?? )(7+?? ) 
? The equation of two systems of generating lines are : 
(
?? 2
-?? )=?? (7-?? ),?? (
?? 2
+?? )=(7+?? ) (1)
(
?? 2
-?? )=?? (7+?? ),?? (
?? 2
+?? )=(7-?? ) (2)
 
(1) and (2) pass through (10,5,1) and (14,2,-2) for ?? =2,?? =
1
3
 and ?? =
9
5
,?? =1. 
So, the two systems of generating lines are 
(
?? 2
-?? )=2(7-?? ), (
?? 2
+?? )=7+?? (3)
(
?? 2
-?? )=
1
3
(7+?? ),
1
3
(
?? 2
+?? )=7-?? (4)
(
?? 2
-?? )=
9
5
(7-?? ),
9
5
(
?? 2
+2)=7+?? (5)
(
?? 2
-?? )=1(7+?? ),
?? 2
+?? =7-?? (6)
 
Solving (3) and (6), we get the vertices as (14,
7
3
,-
7
3
) . 
Solving (4) and (5), we get the vertices as (
21
2
,
77
16
,
21
16
) . 
? Other two vertices are (14,
7
3
,-
7
3
) and (
21
2
,
77
16
,
21
16
) . 
8.2 Show that the generators through any one of the ends of an equiconjugate 
diameter of the principal elliptic section of the hyperboloid 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? are 
inclined to each other at an angle of ????
°
 if ?? ?? +?? ?? =?? ?? ?? . Find also the condition 
for the generators to be perpendicular to each other. 
(2011 : 20 Marks) 
Solution: 
Let ( ?? cos ?? ,?? sin ?? ,0 ) be the given point on the diameter. 
The equations of the two generators through this point are 
?? -?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±?? 
The direction ratios of two generators are (?? sin ?? ,-?? cos ?? ,?? ) and (?? sin ?? ,-?? cos ?? ,-?? ) 
respectively. 
Let ?? be the angle between two generators and let ?? be the parameter of the end points 
of conjugate diameters. 
 cos ?? =
?? 1
?? 2
+?? 1
?? 2
+?? 1
?? 2
v?? 1
2
:?? 1
2
+?? 1
2
v?? 2
2
+?? 2
2
+?? 2
2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 
Putting ?? =60
°
 and ?? =45
°
 ( ? equi-conjugal diameters means equal length of conjugal 
diameters, l.e., v?? 2
cos
2
 ?? +?? 2
sin
2
 ?? which is equal to v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? and is 
possible for ?? =45
°
 ). 
? from (i), we get 
                                 cos 60
°
=
?? 2
2
+
?? 2
2
-?? 2
?? 2
2
+
?? 2
2
+?? 2
 ?                                      
1
2
=
?? 2
+?? 2
-2?? 2
?? 2
+?? 2
+2?? 2
 ?              ?? 2
+?? 2
+2?? 2
=2?? 2
+2?? 2
-4?? 2
 ?                          ?? 2
+?? 2
=6?? 2
 
Again, put ?? =90
°
 and ?? =45
°
 in (i), we get 
0=
?? 2
2
+
?? 2
2
-?? 2
?? 2
2
+
?? 2
2
+?? 2
 
?                                                       ?? 2
+?? 2
=2?? 2
, 
which is the required condition for the generators to be perpendicular to each other. 
8.3 A variable generator meets two generators of the same system through the 
extremities ?? and ?? '
 of the minor axis of the principal elliptic section of the 
hyperboloid 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? in ?? and ?? '
. Prove that ?? ?? '
·?? '
?? '
=?? ?? +?? ?? . 
(Note: There is minor error in actual question. It must be 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? or ???? ·
?? '
?? =?? ?? +
?? ?? ?? ). 
(2012 : 20 Marks) 
Solution: 
The generator through any general point (?? cos ?? ,?? sin ?? ) on the principal elliptic section is 
                                       
?? -?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±??                                         (??)(?????? h ?????????????? ) 
Taking the positive system for the extremity of minor axis ?? =
?? 2
 and 
3?? 2
 
i.e.,                                              
?? -?? ?? =
?? -?? 0
=
?? ??                              (ii) 
and 
?? -?? =
?? +?? 0
=
?? ?? (?????? )
 
Any point on these lines is 
?? ?? =
?? -?? ?? =
?? ?? =?? and 
?? -?? =
?? +?? 0
=
?? ?? =?? 2
?? =???? ,?? =?? ,?? =?? ?? 1
 and ?? =-???? ,?? =-?? ,?? =?? ?? 2
 
Note that the distance of such a point from ?? is v2
2
+?? 2
+?? 2
?? 1
=v?? 2
+?? 2
?? 1
. 
For, ?? ,?? this general point must bs on the variable generaior whose equation is given by 
(i) (taking the other system). 
Page 4


Edurev123 
8. Hyperboloid of One and Two Sheets and 
its Properties 
8.1 Find the vertices of the skew quadrilateral formed by the four generators of the 
hyperboloid 
?? ?? ?? +?? ?? -?? ?? =???? 
passing through (???? ,?? ,?? ) and (???? ,?? ,-?? ) . 
(2010 : 20 Marks) 
Solution: 
Given, the equation of hyperboloid is 
?? 2
4
+?? 2
-?? 2
=49 
It can be rewritten as 
(
?? 2
-?? )(
?? 2
+?? )=(7-?? )(7+?? ) 
? The equation of two systems of generating lines are : 
(
?? 2
-?? )=?? (7-?? ),?? (
?? 2
+?? )=(7+?? ) (1)
(
?? 2
-?? )=?? (7+?? ),?? (
?? 2
+?? )=(7-?? ) (2)
 
(1) and (2) pass through (10,5,1) and (14,2,-2) for ?? =2,?? =
1
3
 and ?? =
9
5
,?? =1. 
So, the two systems of generating lines are 
(
?? 2
-?? )=2(7-?? ), (
?? 2
+?? )=7+?? (3)
(
?? 2
-?? )=
1
3
(7+?? ),
1
3
(
?? 2
+?? )=7-?? (4)
(
?? 2
-?? )=
9
5
(7-?? ),
9
5
(
?? 2
+2)=7+?? (5)
(
?? 2
-?? )=1(7+?? ),
?? 2
+?? =7-?? (6)
 
Solving (3) and (6), we get the vertices as (14,
7
3
,-
7
3
) . 
Solving (4) and (5), we get the vertices as (
21
2
,
77
16
,
21
16
) . 
? Other two vertices are (14,
7
3
,-
7
3
) and (
21
2
,
77
16
,
21
16
) . 
8.2 Show that the generators through any one of the ends of an equiconjugate 
diameter of the principal elliptic section of the hyperboloid 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? are 
inclined to each other at an angle of ????
°
 if ?? ?? +?? ?? =?? ?? ?? . Find also the condition 
for the generators to be perpendicular to each other. 
(2011 : 20 Marks) 
Solution: 
Let ( ?? cos ?? ,?? sin ?? ,0 ) be the given point on the diameter. 
The equations of the two generators through this point are 
?? -?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±?? 
The direction ratios of two generators are (?? sin ?? ,-?? cos ?? ,?? ) and (?? sin ?? ,-?? cos ?? ,-?? ) 
respectively. 
Let ?? be the angle between two generators and let ?? be the parameter of the end points 
of conjugate diameters. 
 cos ?? =
?? 1
?? 2
+?? 1
?? 2
+?? 1
?? 2
v?? 1
2
:?? 1
2
+?? 1
2
v?? 2
2
+?? 2
2
+?? 2
2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 
Putting ?? =60
°
 and ?? =45
°
 ( ? equi-conjugal diameters means equal length of conjugal 
diameters, l.e., v?? 2
cos
2
 ?? +?? 2
sin
2
 ?? which is equal to v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? and is 
possible for ?? =45
°
 ). 
? from (i), we get 
                                 cos 60
°
=
?? 2
2
+
?? 2
2
-?? 2
?? 2
2
+
?? 2
2
+?? 2
 ?                                      
1
2
=
?? 2
+?? 2
-2?? 2
?? 2
+?? 2
+2?? 2
 ?              ?? 2
+?? 2
+2?? 2
=2?? 2
+2?? 2
-4?? 2
 ?                          ?? 2
+?? 2
=6?? 2
 
Again, put ?? =90
°
 and ?? =45
°
 in (i), we get 
0=
?? 2
2
+
?? 2
2
-?? 2
?? 2
2
+
?? 2
2
+?? 2
 
?                                                       ?? 2
+?? 2
=2?? 2
, 
which is the required condition for the generators to be perpendicular to each other. 
8.3 A variable generator meets two generators of the same system through the 
extremities ?? and ?? '
 of the minor axis of the principal elliptic section of the 
hyperboloid 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? in ?? and ?? '
. Prove that ?? ?? '
·?? '
?? '
=?? ?? +?? ?? . 
(Note: There is minor error in actual question. It must be 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? or ???? ·
?? '
?? =?? ?? +
?? ?? ?? ). 
(2012 : 20 Marks) 
Solution: 
The generator through any general point (?? cos ?? ,?? sin ?? ) on the principal elliptic section is 
                                       
?? -?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±??                                         (??)(?????? h ?????????????? ) 
Taking the positive system for the extremity of minor axis ?? =
?? 2
 and 
3?? 2
 
i.e.,                                              
?? -?? ?? =
?? -?? 0
=
?? ??                              (ii) 
and 
?? -?? =
?? +?? 0
=
?? ?? (?????? )
 
Any point on these lines is 
?? ?? =
?? -?? ?? =
?? ?? =?? and 
?? -?? =
?? +?? 0
=
?? ?? =?? 2
?? =???? ,?? =?? ,?? =?? ?? 1
 and ?? =-???? ,?? =-?? ,?? =?? ?? 2
 
Note that the distance of such a point from ?? is v2
2
+?? 2
+?? 2
?? 1
=v?? 2
+?? 2
?? 1
. 
For, ?? ,?? this general point must bs on the variable generaior whose equation is given by 
(i) (taking the other system). 
 ?                                    
?? ?? 1
-?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =-?? 1
 and                             
-?? ?? 1
-?? cos ?? ?? sin ?? =
-?? -?? sin ?? -?? cos ?? =-?? 2
 ?                                                         ?? 1
=
cos ?? 1+sin ??                                                                ?? 2
=-(
1+sin ?? cos ?? )
 ?                                                         ???? =v?? 2
+?? 2
|?? 1
|
                                                           ?? '
?? '
=v?? 2
+?? 2
|?? 2
|
 ?                                             ???? ·?? '
?? '
=(?? 2
+?? 2
)
cos ?? 1+sin ?? ×
1+sin ?? cos ??                                                                     =?? 2
+?? 2
 
8.4 Find the equations of the two generating lines through any point 
(?? ?????? ?? ,?? ?????? ?? ,?? ) , of the principal elliptic section 
?? ?? ?? ?? +
?? ?? ?? ?? =?? ,?? =?? , of the 
hyperboloid by the plane ?? =?? . 
(2014 : 15 Marks) 
Solution: 
Any point on the elliptic section of the hyperboloid is (?? cos ?? ,?? sin ?? ,0) . 
? Equations of any line through this point is 
?? -?? cos ?? ?? =
?? -?? sin ?? ?? =
?? -0
?? =?? ( say ) (??)
 
Any point on this line is (???? +?? cos ?? ,???? +?? sin ?? , and it lies on given hyperboloid, if 
(???? +?? cos ?? )
2
?? 2
+
(???? +?? sin ?? )
2
?? 2
-
?? 2
?? 2
?? 2
 =1
 or                                 (
?? 2
?? 2
+
?? 2
?? 2
-
?? 2
?? 2
)?? 2
+2(
??cos ?? ?? +
?? sin ?? ?? )?? =0                                     (???? )
 
If the line (i) generator of given hyperboloid, then (i) lies wholly on the hyperboloid and 
the condition for which from (ii) are 
(
?? 2
?? 2
)+(
?? 2
?? 2
)-(
?? 2
?? 2
) =0 (?????? )
??cos ?? ?? +
?? sin ?? ?? =0 (???? )
 
from (iv) we get, 
Page 5


Edurev123 
8. Hyperboloid of One and Two Sheets and 
its Properties 
8.1 Find the vertices of the skew quadrilateral formed by the four generators of the 
hyperboloid 
?? ?? ?? +?? ?? -?? ?? =???? 
passing through (???? ,?? ,?? ) and (???? ,?? ,-?? ) . 
(2010 : 20 Marks) 
Solution: 
Given, the equation of hyperboloid is 
?? 2
4
+?? 2
-?? 2
=49 
It can be rewritten as 
(
?? 2
-?? )(
?? 2
+?? )=(7-?? )(7+?? ) 
? The equation of two systems of generating lines are : 
(
?? 2
-?? )=?? (7-?? ),?? (
?? 2
+?? )=(7+?? ) (1)
(
?? 2
-?? )=?? (7+?? ),?? (
?? 2
+?? )=(7-?? ) (2)
 
(1) and (2) pass through (10,5,1) and (14,2,-2) for ?? =2,?? =
1
3
 and ?? =
9
5
,?? =1. 
So, the two systems of generating lines are 
(
?? 2
-?? )=2(7-?? ), (
?? 2
+?? )=7+?? (3)
(
?? 2
-?? )=
1
3
(7+?? ),
1
3
(
?? 2
+?? )=7-?? (4)
(
?? 2
-?? )=
9
5
(7-?? ),
9
5
(
?? 2
+2)=7+?? (5)
(
?? 2
-?? )=1(7+?? ),
?? 2
+?? =7-?? (6)
 
Solving (3) and (6), we get the vertices as (14,
7
3
,-
7
3
) . 
Solving (4) and (5), we get the vertices as (
21
2
,
77
16
,
21
16
) . 
? Other two vertices are (14,
7
3
,-
7
3
) and (
21
2
,
77
16
,
21
16
) . 
8.2 Show that the generators through any one of the ends of an equiconjugate 
diameter of the principal elliptic section of the hyperboloid 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? are 
inclined to each other at an angle of ????
°
 if ?? ?? +?? ?? =?? ?? ?? . Find also the condition 
for the generators to be perpendicular to each other. 
(2011 : 20 Marks) 
Solution: 
Let ( ?? cos ?? ,?? sin ?? ,0 ) be the given point on the diameter. 
The equations of the two generators through this point are 
?? -?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±?? 
The direction ratios of two generators are (?? sin ?? ,-?? cos ?? ,?? ) and (?? sin ?? ,-?? cos ?? ,-?? ) 
respectively. 
Let ?? be the angle between two generators and let ?? be the parameter of the end points 
of conjugate diameters. 
 cos ?? =
?? 1
?? 2
+?? 1
?? 2
+?? 1
?? 2
v?? 1
2
:?? 1
2
+?? 1
2
v?? 2
2
+?? 2
2
+?? 2
2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 =
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? -?? 2
?? 2
sin
2
 ?? +?? 2
cos
2
 ?? +?? 2
 
Putting ?? =60
°
 and ?? =45
°
 ( ? equi-conjugal diameters means equal length of conjugal 
diameters, l.e., v?? 2
cos
2
 ?? +?? 2
sin
2
 ?? which is equal to v?? 2
sin
2
 ?? +?? 2
cos
2
 ?? and is 
possible for ?? =45
°
 ). 
? from (i), we get 
                                 cos 60
°
=
?? 2
2
+
?? 2
2
-?? 2
?? 2
2
+
?? 2
2
+?? 2
 ?                                      
1
2
=
?? 2
+?? 2
-2?? 2
?? 2
+?? 2
+2?? 2
 ?              ?? 2
+?? 2
+2?? 2
=2?? 2
+2?? 2
-4?? 2
 ?                          ?? 2
+?? 2
=6?? 2
 
Again, put ?? =90
°
 and ?? =45
°
 in (i), we get 
0=
?? 2
2
+
?? 2
2
-?? 2
?? 2
2
+
?? 2
2
+?? 2
 
?                                                       ?? 2
+?? 2
=2?? 2
, 
which is the required condition for the generators to be perpendicular to each other. 
8.3 A variable generator meets two generators of the same system through the 
extremities ?? and ?? '
 of the minor axis of the principal elliptic section of the 
hyperboloid 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? in ?? and ?? '
. Prove that ?? ?? '
·?? '
?? '
=?? ?? +?? ?? . 
(Note: There is minor error in actual question. It must be 
?? ?? ?? ?? +
?? ?? ?? ?? -
?? ?? ?? ?? =?? or ???? ·
?? '
?? =?? ?? +
?? ?? ?? ). 
(2012 : 20 Marks) 
Solution: 
The generator through any general point (?? cos ?? ,?? sin ?? ) on the principal elliptic section is 
                                       
?? -?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±??                                         (??)(?????? h ?????????????? ) 
Taking the positive system for the extremity of minor axis ?? =
?? 2
 and 
3?? 2
 
i.e.,                                              
?? -?? ?? =
?? -?? 0
=
?? ??                              (ii) 
and 
?? -?? =
?? +?? 0
=
?? ?? (?????? )
 
Any point on these lines is 
?? ?? =
?? -?? ?? =
?? ?? =?? and 
?? -?? =
?? +?? 0
=
?? ?? =?? 2
?? =???? ,?? =?? ,?? =?? ?? 1
 and ?? =-???? ,?? =-?? ,?? =?? ?? 2
 
Note that the distance of such a point from ?? is v2
2
+?? 2
+?? 2
?? 1
=v?? 2
+?? 2
?? 1
. 
For, ?? ,?? this general point must bs on the variable generaior whose equation is given by 
(i) (taking the other system). 
 ?                                    
?? ?? 1
-?? cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =-?? 1
 and                             
-?? ?? 1
-?? cos ?? ?? sin ?? =
-?? -?? sin ?? -?? cos ?? =-?? 2
 ?                                                         ?? 1
=
cos ?? 1+sin ??                                                                ?? 2
=-(
1+sin ?? cos ?? )
 ?                                                         ???? =v?? 2
+?? 2
|?? 1
|
                                                           ?? '
?? '
=v?? 2
+?? 2
|?? 2
|
 ?                                             ???? ·?? '
?? '
=(?? 2
+?? 2
)
cos ?? 1+sin ?? ×
1+sin ?? cos ??                                                                     =?? 2
+?? 2
 
8.4 Find the equations of the two generating lines through any point 
(?? ?????? ?? ,?? ?????? ?? ,?? ) , of the principal elliptic section 
?? ?? ?? ?? +
?? ?? ?? ?? =?? ,?? =?? , of the 
hyperboloid by the plane ?? =?? . 
(2014 : 15 Marks) 
Solution: 
Any point on the elliptic section of the hyperboloid is (?? cos ?? ,?? sin ?? ,0) . 
? Equations of any line through this point is 
?? -?? cos ?? ?? =
?? -?? sin ?? ?? =
?? -0
?? =?? ( say ) (??)
 
Any point on this line is (???? +?? cos ?? ,???? +?? sin ?? , and it lies on given hyperboloid, if 
(???? +?? cos ?? )
2
?? 2
+
(???? +?? sin ?? )
2
?? 2
-
?? 2
?? 2
?? 2
 =1
 or                                 (
?? 2
?? 2
+
?? 2
?? 2
-
?? 2
?? 2
)?? 2
+2(
??cos ?? ?? +
?? sin ?? ?? )?? =0                                     (???? )
 
If the line (i) generator of given hyperboloid, then (i) lies wholly on the hyperboloid and 
the condition for which from (ii) are 
(
?? 2
?? 2
)+(
?? 2
?? 2
)-(
?? 2
?? 2
) =0 (?????? )
??cos ?? ?? +
?? sin ?? ?? =0 (???? )
 
from (iv) we get, 
                    
?? asin ?? =
?? -?? cos ?? or 
(??/?? )
sin ?? =
(?? /-?? )
cos ?? ?                
(??/?? )
sin ?? =
(?? /-?? )
cos ?? =v
(?? 2
/?? 2
)+(?? 2
/?? 2
)
vsin
2
 ?? +cos
2
 ?? =
v?? 2
/?? 2
1
 ?             
?? ?? sin ?? =
?? -?? cos ?? =
?? ±?? 
? The equation to the required generated from (i) are 
?? -cos ?? ?? sin ?? =
?? -?? sin ?? -?? cos ?? =
?? ±?? 
8.5. Find all the asymptotes of the curve (?? ?? +?? )?? =(?? -?? )
?? . 
(2020: 10 marks) 
Solution: 
Here the given curve (2?? -3)?? =(?? -1)
2
 
2???? -3?? =?? 2
-2?? +1
?? 2
-2???? -2?? -3?? +1 =0
 
Putting                                                                            ?? =???? +?? 
?? 2
-[2?? (???? +?? )]-2?? -3(???? +?? )+1=0 
?? 2
-2?? 2
?? -2???? -2?? -3???? -3?? +1=0 
(1-2?? )?? 2
-?? (2?? +2+3?? )-3?? +1=0 
Putting coefficient of ?? 2
=0 and ?? =0 
1-2?? =0
?? =1/2
2?? +2+3?? =0
 
2?? +2+3×
1
2
 =0
2?? +
4+3
2
 =0
2?? +
7
2
 =0
?? =-
7
4
 
Thus ?? =
?? 2
-
7
2
 is one asymptote. Equating highest power equal to zero. We get 
asymptotes parallel to ?? -axis. 
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