- #1

- 5

- 0

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter redoxes
- Start date

- #1

- 5

- 0

- #2

tiny-tim

Science Advisor

Homework Helper

- 25,832

- 251

Draw a circle in a paper, if the line of sight perpendular to the paper , we see a circle ,but if the line of sight is not perpendular to the paper, must we see an ellipse ? how to prove it ? how to find out the major axis or minor axis ? It seem that when we observe the circle ,it should be wide in near place and narrow in far place and should look like a chicken egg ,but it is not true ,how to explain the contradiction.

Hi redoxes! Welcome to PF!

Proof that a circle viewed obliquely is an ellipse depends on how you define an ellipse.

The easiest way is to define it as a conic section, that is as the intersection of a plane and an upright circular cone …

then you can prove it using Dandelin spheres …

see the PF LIbrary on https://www.physicsforums.com/library.php?do=view_item&itemid=98"

Last edited by a moderator:

Share: