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11th Grade > Mathematics

CONIC SECTIONS MCQs

Total Questions : 30 | Page 3 of 3 pages
Question 21.


If a circle whose centre is (1, –3) touches the line 3x – 4y –5 = 0, then the radius of the circle is


  1.     2
  2.     4
  3.     52
  4.     72
 Discuss Question
Answer: Option A. -> 2
:
A

Radius = perpendicular distance from (1, -3) to the given line 3x - 4y - 5 = 0.
i.e. 3+12552=2.


Question 22.


The area of the circle whose centre is at (1, 2) and which passes through the point (4, 6) is


  1.     5π
  2.     10π
  3.     25π
  4.     None of these
 Discuss Question
Answer: Option C. -> 25π
:
C

Radius = (14)2+(26)2=5
Hence the area is given by πr2=25π sq. units.


Question 23.


The equation of the parabola with its vertex at the origin, axis on the y-axis and passing through the point (6, -3) is   


  1.     y3=12x+6 
  2.     x2=12y 
  3.     x2=12y 
  4.     y2=12x+6 
 Discuss Question
Answer: Option C. -> x2=12y 
:
C

Since the axis of parabola is y-axis 


Equation of parabola x2=4ay 


Since it passes through (6 , -3)


36 = -12 a a=3 


Equation of parabola is x2=12y .
Question 24.


The co-ordinates of the extremities of the latus rectum of the parabola 5y2=4x are 


  1.     (15.25),(15,25)
  2.     (15.25),(15,25)
  3.     (15.45),(15,45)
  4.     None of these
 Discuss Question
Answer: Option B. -> (15.25),(15,25)
:
B

y2=4.15x;a=15 . Focus is (15,0) and co-ordinates of latus rectum are y2=425y=±25 


or end points of latus rectum are (15,±25)


Question 25.


The distance between the directrices of the hyperbola x2y2=9 is ___ .


  1.     92
  2.     32
  3.     62
  4.     32
 Discuss Question
Answer: Option D. -> 32
:
D

The given hyperbola is x2y2=9
x29y29=1
a=3, b=3, c=a2+b2=32
The equation of  the directrices are x=±a2c
Distance between directrices,
d=2a2c=1832=32


Question 26.


If the eccentricity of the hyperbola x2a2y2b2=1 is 5/4 and 2x+3y-6 = 0 is a focal chord of the hyperbola, then the length of the transverse axis is equal to ___ .


  1.     125
  2.     127
  3.     245
  4.     247
 Discuss Question
Answer: Option C. -> 245
:
C

The hyperbola is of the form 
x2a2y2b2=1


The transverse axis of the hyperbola is along the x-axis. Given that 2x + 3y-6=0 is a focal chord. Let (c,0) be the focus.
2c+06=0c=3Given, e=54 a=ce=125


The length of the transverse axis is 2a=245


Question 27.


A point P on the ellipse is at a distance of 6 units from the focus. If the eccentricity of the ellipse is 0.6, then the distance of P from the corresponding directrix is ___


 Discuss Question
Answer: Option C. -> 245
:

The eccentricity of any conic is the ratio of its distances from the focus and directrix. Let d be the distance of the point P from the directrix. Since P lies on the ellipse,


6d=35d=10


Question 28.


The length of the transverse axis of a hyperbola is 2cos t. The foci of the hyperbola are the same as that of the ellipse 9x2+16y2=144.
The equation of the hyperbola is ___


  1.     x2cos2ty27cos2t=1
  2.     x2cos2ty27+cos2t=1
  3.     x21+cos2ty27cos2t=1
  4.     x21+cos2ty27+cos2t=1
 Discuss Question
Answer: Option A. -> x2cos2ty27cos2t=1
:
A

For the given hyperbola, Length of the transverse axis = 2a
2a= 2cos ta = cos t


Consider the ellipse


9x2+16y2=144x216+y29=1Focal length, c=169=7


This is the same as the focal length of the hyperbola.


Now, for the hyperbola,
b2=c2a2b2=7cos2t


The equation of the hyperbola is
x2cos2ty27cos2t=1


Question 29.


The foci of the ellipse x225+y2b2=1 and the hyperbola x2144+y225=113 are the same.


The value of b2 is ___ .


 Discuss Question
Answer: Option A. -> x2cos2ty27cos2t=1
:

Consider the following hyperbola


x2144y225=11313 x214413 y225=1a2=14413; b2=2513Focal length, c=a2+b2c=144+2513=16913=13


Also, this is the focus of the ellipse 
x225+y2b2=1c2=a2b213=25b2b2=12


Question 30.


The length of the latus rectum and the length of the transverse axis of a hyperbola are 43 & 23 respectively, then the equation of the hyperbola can be


  1.     x23y26=1
  2.     x23y29=1
  3.     x26y29=1
  4.     x26y23=1
 Discuss Question
Answer: Option A. -> x23y26=1
:
A

Let the transverse axis be along the x-axis such that the hyperbola is of the form


x2a2y2b2=1
Latus Rectum = 2b2a=43
Also, 2a=23a=3


2b23=43b2=6


The equation of the hyperbola is


x23y26=1


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