An ellipse question?

  • #1
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i added a file with the curve the is being asked to find

an ellipse is given. its formula is x^2 + 2*y^2=8 .

find the formula of the curve that is being created by the

the centers of the perpendicular lines to the X axes and the ellipse.


i tried to solve this question
by putting the Y^2 on the one side and on the other the rest
and devidind it by 2 .


2y^2=8-x^2
y^2=8-x^2/2
y=V(8-x^2/2)
(v=root simbol)

the curve that in the center always smaller in height by 2
so i devided the formula by 2 to find our curve

y=1/2*V(8-x^2/2)
in my book it gives a different answer

(x^2)/8 +y^2=1

plz help
 

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Answers and Replies

  • #2
HallsofIvy
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What do you mean by "the centers of the perpendicular lines to the X axes and the ellipse"?
 
  • #3
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like it shows at the pictue
a curve wich composed from the middle points of this straight lines
parrallel to the Y axes
 
  • #4
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0
how can i solve this thing???
 
  • #5
HallsofIvy
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[itex]x^2+ 2y^2= 8[/itex] is the same as [itex]\frac{x^2}{8}+ \frac{y^2}{4}= 1[/itex].
That's an ellipse with major semi-axis, along the x-axis, of length [itex]\sqrt{8}= 2\sqrt{2}[/itex] and minor semi-axis, along the y-axis, of length 2.

Dividing the y-coordinate of each point by 2 gives an ellipse with the same major semi-axis but minor semi-axis of length 1:
[itex]\frac{x^2}{8}+ y^2=1[/itex].
 
  • #6
HallsofIvy
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i added a file with the curve the is being asked to find

an ellipse is given. its formula is x^2 + 2*y^2=8 .

find the formula of the curve that is being created by the

the centers of the perpendicular lines to the X axes and the ellipse.


i tried to solve this question
by putting the Y^2 on the one side and on the other the rest
and devidind it by 2 .


2y^2=8-x^2
y^2=8-x^2/2
Here's your error! Don't know why I didn't see this sooner. Dividing both sides of 2y2= 8- x2 by 2 gives y2= 4- x2!

y=V(8-x^2/2)
(v=root simbol)

the curve that in the center always smaller in height by 2
so i devided the formula by 2 to find our curve

y=1/2*V(8-x^2/2)
[itex]y= 1/2 \sqrt{4- x^2}[/itex]

in my book it gives a different answer

(x^2)/8 +y^2=1

plz help
Square both sides of [itex]2y= \sqrt{4- x^2}[/itex] and you get
[itex]4y^2= 4- x^2[/itex] or [itex]x^2+ 4y^2= 4[/itex].

Divide through by 4:
[tex]\frac{x^2}{4}+ y^2= 1[/itex]
 
  • #8
HallsofIvy
Science Advisor
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Now, my question is, "what does this have to do with 'Tensor Analysis and Differential Geometry'?"
 

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