Normal to a fixed concentric ellipse

In summary: OK, nearly there. Now you must set a' and b' so that all values of θ and α can occur. (Otherwise there will be a gap in one of the ellipses.)a'=sec\phi a'=sec\phib'=cosec\phi b'=cosec\phia'=b'=0 a'=b'=0a'=sec\phi a'=sec\phib'=cosec\phi b'=cosec\phia'=b'=sec\phi a'=b'=sec\phia'=sec\phi a'=
  • #1
utkarshakash
Gold Member
854
13

Homework Statement


PM and PN are perpendiculars upon the axes from any point 'P' on the ellipse. Prove that MN is always normal to a fixed concentric ellipse

Homework Equations



The Attempt at a Solution


I assume point P to be (acosθ, bsinθ)

The eqn of line MN is then given by
[itex] bsin\theta x+acos\theta y =absin\theta cos\theta[/itex]
 
Physics news on Phys.org
  • #2
Try writing the generic equation for a normal to an ellipse with same centre and axes.
 
  • #3
haruspex said:
Try writing the generic equation for a normal to an ellipse with same centre and axes.

[itex]a'sec \phi x - b'cosec \phi y = a^2 - b^2[/itex]
 
  • #4
utkarshakash said:
[itex]a'sec \phi x - b'cosec \phi y = a^2 - b^2[/itex]
I assume you meant [itex]a'sec \phi x - b'cosec \phi y = a'^2 - b'^2[/itex]
It remains to find expressions for a', b' and phi in terms of a, b and θ that make this the same as the equation for MN. There is a constraint regarding which of a', b' and phi can depend on which of a, b and θ.
 
  • #5
haruspex said:
I assume you meant [itex]a'sec \phi x - b'cosec \phi y = a'^2 - b'^2[/itex]
It remains to find expressions for a', b' and phi in terms of a, b and θ that make this the same as the equation for MN. There is a constraint regarding which of a', b' and phi can depend on which of a, b and θ.

Do you want me to compare the two lines?
 
  • #6
utkarshakash said:
Do you want me to compare the two lines?
Yes. You want to make a′x sec(ϕ)−b′y cosec(ϕ)=a′2−b′2 look like bx sin(θ)+ay cos(θ)=ab sinθ cosθ by suitable choices of a', b' and ϕ. But note that this must work keeping a' and b' fixed while ϕ is allowed to vary as a function of θ.
 
  • #7
haruspex said:
Yes. You want to make a′x sec(ϕ)−b′y cosec(ϕ)=a′2−b′2 look like bx sin(θ)+ay cos(θ)=ab sinθ cosθ by suitable choices of a', b' and ϕ. But note that this must work keeping a' and b' fixed while ϕ is allowed to vary as a function of θ.

OK I did exactly what you said and got the following relations after comparison

[itex] cos\alpha = \dfrac{aa'cos\theta}{a'^2 - b'^2} \\

sin \alpha = \dfrac{-bb'sin\theta}{a'^2 - b'^2} \\

tan \alpha = \dfrac{-bb' tan\theta}{aa'}

[/itex]
 
  • #8
utkarshakash said:
OK I did exactly what you said and got the following relations after comparison

[itex] cos\alpha = \dfrac{aa'cos\theta}{a'^2 - b'^2} \\

sin \alpha = \dfrac{-bb'sin\theta}{a'^2 - b'^2} \\

tan \alpha = \dfrac{-bb' tan\theta}{aa'}

[/itex]
OK, nearly there. Now you must set a' and b' so that all values of θ and α can occur. (Otherwise there will be a gap in one of the ellipses.)
 

Related to Normal to a fixed concentric ellipse

1. What is a fixed concentric ellipse?

A fixed concentric ellipse is a geometric shape that consists of two axes (major and minor) that intersect at a fixed point, known as the center. The shape of the ellipse remains constant no matter where it is located on the plane.

2. How is normal defined for a fixed concentric ellipse?

The normal for a fixed concentric ellipse is a line that is perpendicular to the tangent at any point on the ellipse. This means that the normal intersects the tangent at a 90-degree angle.

3. How is the normal to a fixed concentric ellipse calculated?

The normal to a fixed concentric ellipse can be calculated using the derivative of the ellipse's equation. The derivative at any given point on the ellipse will give the slope of the tangent, and the negative reciprocal of this slope will give the slope of the normal.

4. What is the significance of the normal to a fixed concentric ellipse?

The normal to a fixed concentric ellipse can be used to determine the curvature of the ellipse at any given point. It is also important in many engineering applications, such as in the design of gears and pulleys.

5. How does the normal to a fixed concentric ellipse change with varying eccentricity?

The eccentricity of an ellipse, which is a measure of how elongated or circular it is, affects the shape and orientation of the normal. As the eccentricity increases, the normal approaches the minor axis and becomes more parallel to it.

Similar threads

  • Precalculus Mathematics Homework Help
Replies
3
Views
2K
  • Precalculus Mathematics Homework Help
Replies
7
Views
5K
  • Precalculus Mathematics Homework Help
Replies
18
Views
2K
  • Precalculus Mathematics Homework Help
Replies
8
Views
3K
  • Calculus and Beyond Homework Help
Replies
1
Views
1K
Replies
4
Views
599
  • Calculus and Beyond Homework Help
Replies
2
Views
1K
  • Precalculus Mathematics Homework Help
Replies
6
Views
4K
  • Calculus and Beyond Homework Help
Replies
2
Views
2K
  • Topology and Analysis
Replies
2
Views
1K
Back
Top