Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Is MIT's Larry Guth, Sigurdur Helgason, Anette Hosoi as dumb as Dan
Christensen in thinking ellipse is a conic section when it really is an OVAL
(proofs at end of post)

Replies: 5   Last Post: Oct 5, 2017 5:04 PM

 Messages: [ Previous | Next ]
 Me Posts: 1,716 Registered: 1/23/16
Re: Is MIT's Larry Guth, Sigurdur Helgason, Anette Hosoi as dumb as
Dan Christensen in thinking ellipse is a conic section when it really is an
OVAL (proofs at end of post)

Posted: Oct 3, 2017 12:14 PM

On Tuesday, October 3, 2017 at 3:17:50 PM UTC+2, Archimedes Plutonium wrote:

> Here Franz is muddling through a mess

With *a little efford* the significance of the formulas (the calculation) can be figured out. You know, math is not just bla bla.

> not knowing what is a circle from oval

You obviously don't know the general equation for an ellipse.

Hint:

(1/ab)y^2 + (4/h^2)(x - h/2)^2 = 1

is the equation for an ellipse.

If a = b = r and h = 2r we get the equation of a circle:

(1/r^2)y^2 + (1/r^2)(x - r)^2 = 1

=> (x - r)^2 + y^r = r^2

Are you really too dumb to understand these simple things, Archie?

Here's the complete proof again:

> > Cone/Cylinder (side view):
> >
> > / | \ (with b <= a)
> > /b | \
> > /---+---´ <= x = h
> > / |´ \
> > / ´ | \
> > / ´ | \
> > x = 0 => ´-------+-------\
> > / a | \
> >
> > (cone: b < a, cylinder: b = a = r)
> >
> > r(x) = a - ((a-b)/h)x
> > d(x) = a - ((a+b)/h)x
> >
> > y(x)^2 = r(x)^2 - d(x)^2 = ab - ab(2x/h - 1)^2 = ab(1 - 4(x - h/2)^2/h^2
> >
> > => (1/ab)y(x)^2 + (4/h^2)(x - h/2)^2 = 1 ...equation of an ellipse

qed.

Now lets just look at some "properties" of this ellipse:

> > Some considerations:
> >
> > => y(h/2 + x')^2 = ab - ab(2(h/2 + x')/h - 1)^2 = ab - ab(2x'/h)^2
> >
> > => y(h/2 + x') = sqrt(ab) * (sqrt(1 - (2x'/h)^2) ...symmetric relative to h/2 (hence Ec = cF)
> >
> > => y(h/2) = sqrt(ab) (= Gc = cH)

Date Subject Author
10/3/17 plutonium.archimedes@gmail.com
10/3/17 Dan Christensen
10/3/17 Me
10/3/17 Me
10/5/17 plutonium.archimedes@gmail.com
10/5/17 Me