Zeros of polynomial vs derivative

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Dr Peyam

Dr Peyam

Күн бұрын

We will see how the zeros of the derivative of a polynomial are related to the zeros of the original polynomial. This is called the Gauss Lucas Theorem for zeros of derivatives, which is an elegant result from complex analysis that relates it with the convex hull of the original roots. I also mention Marden's theorem, which is a special case of a triangle, and which has to do with the Steiner inellipse and foci. Enjoy this geometry and calculus adventure.
0:00 Introduction
0:09 Roots of P
3:00 Plotting the roots geometrically
5:15 Gauss Lucas Theorem
6:52 Marden's Theorem
Gauss Lucas (full version): • Gauss Lucas Theorem (o... (members only)
Gauss Lucas Proof: • Gauss Lucas Proof (members only)
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Пікірлер: 92
@muriloporfirio7853
@muriloporfirio7853 2 жыл бұрын
And also, the average of the roots of P is the average of the roots of P'. Not sure about the name of this theorem but it is also really cool.
@User-gt1lu
@User-gt1lu 2 жыл бұрын
I am not sure if it has a name but it is a consequence of Vieta‘s Theorem.
@sharpnova2
@sharpnova2 2 жыл бұрын
i was the one who discovered this. it's called sharp's lemma, and was a lemma for proving collatz, which i also did
@michaelempeigne3519
@michaelempeigne3519 2 жыл бұрын
@@sharpnova2 sharp's lemma does not bring up anything when i google it.
@Thitadhammo
@Thitadhammo 2 жыл бұрын
I suppose if anyone had solved the Collatz conjecture, this would be widely known. We're talking the 3n+1 game, right? Terence Tao came pretty close three years or so ago. I, sir, call shenanigans.
@pierrestober3423
@pierrestober3423 2 жыл бұрын
What if he proved it but the proof doesn't fit in a KZfaq comment ?
@Galileosays
@Galileosays 2 жыл бұрын
Wow. This puts a new light on the cubic equations of state, where the derivatives are essential in finding the liquid and gas volume at an equilibrium.
@DrBarker
@DrBarker 2 жыл бұрын
This was very cool! I'm always amazed by how much interesting structure there is behind seemingly "simple" topics, like roots of a cubic and its derivative here.
@LouisEmery
@LouisEmery 2 жыл бұрын
So if you add a constant C to the P, the roots change of course, but not those of P'. The roots of P' will remain the foci of any ellipses formed by roots of P + C. Interesting.
@antoniocampos9721
@antoniocampos9721 2 жыл бұрын
Man, this is absolutely awesome from you. You don't stop surprising me.
@ingiford175
@ingiford175 2 жыл бұрын
And if you collapse this to a line (example only real roots), there must be a 0 of the derivative between each real root. Since each line segment between 2 roots is the convex hull. Nice.
@ingiford175
@ingiford175 2 жыл бұрын
Thinking more, is this why Sturm's Method for Counting Real Roots works?
@theproofessayist8441
@theproofessayist8441 2 жыл бұрын
Inellipse is ellipse inscribed within triangle. Personally I hope this term is consistent with ellipses inscribed in other polygons. Good to see you post again Dr. Peyam. We're all busy at work.
@Homayoun197250
@Homayoun197250 2 жыл бұрын
Quite interesting. Dankeschön. مرسی. 😊
@DeanCalhoun
@DeanCalhoun 2 жыл бұрын
amazing!! math is so incredible
@barryzeeberg3672
@barryzeeberg3672 2 жыл бұрын
Can you use the Vieta formulas for the roots (of the original and the derivative), to get a relationship between the roots of the original and the derivative? This might work since there is a simple closed form for the coefficients of the derivative of a polynomial.
@nikhilnagaria2672
@nikhilnagaria2672 2 жыл бұрын
New Dr Peyam upload :DD
@bioengboi137
@bioengboi137 2 жыл бұрын
Then for the cherry on top, the root of P’’ is center of the ellipse which is the midpoint between the roots of P’ (foci). Overall it’s a geometric jewel!
@drpeyam
@drpeyam 2 жыл бұрын
Woooow thank you!!
@H0tinNYC
@H0tinNYC 2 жыл бұрын
I'm not sure why but I find this amazing.
@adityadwivedi4412
@adityadwivedi4412 2 жыл бұрын
Very amazing
@FT029
@FT029 2 жыл бұрын
ha, the gauss-lucas proof was on my homework that was due last week! fun theorem
@obafemiyussuf6864
@obafemiyussuf6864 3 ай бұрын
Thank you sir, I really appreciate your effort in trying to breakdown and explain the calculus topics. I don't know if U can do a video involving csc, cot and other variables in a math problem sir, thanks.
@Happy_Abe
@Happy_Abe 2 жыл бұрын
Peyam is back!
@brendanlawlor2214
@brendanlawlor2214 2 жыл бұрын
omg geometry my weakness prefer algebra but the Lucas hull container of lower differential form is beautiful & l was gobsmacked by the beautiful fact that the interior lower differential roots are foci of an ellipse....a beeeeeudiful property . Dr Peyam the best math guru KZfaq influencer . 🤪👍
@bprpcalculusbasics
@bprpcalculusbasics 2 жыл бұрын
I want a quintic example.
@Jared7873
@Jared7873 2 жыл бұрын
I'm glad you're here! 😀
@adithyan9263
@adithyan9263 2 жыл бұрын
Exactly what was on my Mind
@mj90007
@mj90007 2 жыл бұрын
I don't know anything abt complex numbers But I worked on a similar problem[ 1 month ago] , & the question is can a polynomial function and it's gradient function can have common roots And the answer is yes I have started with linear (..to cubic) I made equations for the coeffs by using theory of eqns And then on solving I came to a conclusion that if the original polynomial have a repeated root , then it's gradient function will share a zero Later, i made it simple If the curve touches just touches the x(at a) axis at any root then f(a)=0 and f'(a)=0 And its just a simple logic , i didn't notice that :)
@qveciana
@qveciana 2 жыл бұрын
Great😀
@jJo663
@jJo663 2 жыл бұрын
7:42 🥁
@shahinjahanlu2199
@shahinjahanlu2199 2 жыл бұрын
Thx
@AndDiracisHisProphet
@AndDiracisHisProphet 2 жыл бұрын
NO WAY!!! Wie geil ist das denn!?
@abdonecbishop
@abdonecbishop 4 ай бұрын
Peyam your magic is inspirational ....... makes me imagine.....seeing two set of planar triangulated roots for cubic polynomial and quadratic polynomials solutions.......whose first derivative and integral polynomial zero point solutions have group symmetries G1((1,2,3)^2)... and ....G2((4,5)^3)...meaning we can interpret....the differential equation integral(G2((4,5)^3)) = derivative(G1((1,2,3)^2)) has a 5 point closed symmetry ...Let's quick summarize..... we put together a pair of zero point calculus functions...and the math looks 'OK' OK.....let's imagine rotating both cubic and quadratic solution zero point roots, so that each root rotates 'pi/2' radians and then assume, all roots share the same angle of parallelism.... look ....a far hand is up........may we ask a physic's question? ......Are the five rotated roots the same as Lagrange's orbital set of 5 orbiting 'stationary' points derived from the symmetry generated by arithmetically combining a pair of calculus connected closed geometries with points mapped to.... or covered by....arithmetic subgroups G1 and G2 analytically extending to a super group G3((G1 * G2) + (G1+ G2))) line endpoint operands [...] calculated using arithmetic field point operations computed on a Gaussian (field point) clock calculator . The super group G3 virtually extends the cubic and quadratic polynomial zero point G1 and G2 solutions factored by both virtual(3D) and real(2D) vector spaces?
@Michael_Fischer
@Michael_Fischer 2 жыл бұрын
this reminds me of the Gershgorin circle theorem. is there a relation?
@drpeyam
@drpeyam 2 жыл бұрын
Interesting!! I didn’t realize there would be a connection
@santiagoferreyra5573
@santiagoferreyra5573 2 жыл бұрын
So the effect of varying the constant term of P would be to rotate the triangle, while maintaining contact whit the elipse?
@drpeyam
@drpeyam 2 жыл бұрын
Wow I didn’t even think about that! Not sure about rotating but the foci surely stay the same
@toaster4693
@toaster4693 2 жыл бұрын
I don't think it could be a rigid transformation like a simple rotation, could it? I'm failing to visualize that.
@jfcrow1
@jfcrow1 2 жыл бұрын
Imaginary roots are complex conjugate so rotation would not work.
@santiagoferreyra5573
@santiagoferreyra5573 2 жыл бұрын
@@jfcrow1 yeah you're right, so i suppose it would transform in some non-trivial way in order to maintain the 3 touching points
@ingiford175
@ingiford175 2 жыл бұрын
Not really since there is a family of ellipses with any given foci. Now it might be interesting to study each individual ellipses (the different d in foci/distance definition) and see how that constrains the constant.
@smurfsmurfy6766
@smurfsmurfy6766 2 жыл бұрын
Does the 2nd theorem generalizes in some way to any degree? Conjectures?
@drpeyam
@drpeyam 2 жыл бұрын
No I think it’s peculiar to 3rd degree polys
@brendanlawlor2214
@brendanlawlor2214 2 жыл бұрын
Higher orders depend on the unknown higher dims if physics
@blacklightning7227
@blacklightning7227 4 ай бұрын
Woa 👌🔥
@draugami
@draugami 2 жыл бұрын
I would like to see this apart from i.
@mickmenn2
@mickmenn2 2 жыл бұрын
Too beautifil
@vaughanwilliamson173
@vaughanwilliamson173 2 жыл бұрын
Not that it affected the presentation much, but I did notice at the start that instead of saying "x^3 minus 4x^2 plus 6x minus 4", the additions and subtractions were transposed. Only a simple oops... and doesn't really detract as the error doesn't resurface. I do enjoy the enthusiasm for the subject!😀
@pesilaratnayake162
@pesilaratnayake162 2 жыл бұрын
So the Gauss Lucas Theorem would lead to each successive derivative having the convex hull of its roots being a subset of the convex of the previous derivative? Would the also apply for collinear sets of roots? E.g., if P(z)=0 has only real solutions, all derivatives of P(z) are guaranteed to only have real solutions?
@drpeyam
@drpeyam 2 жыл бұрын
I think so, although not entirely sure
@DhirajKumar-rx8hi
@DhirajKumar-rx8hi 2 жыл бұрын
Yes Guaranteed...because between any two roots of the P(z) lies the roots of P'(z). Normal Calculus
@pesilaratnayake162
@pesilaratnayake162 2 жыл бұрын
@@DhirajKumar-rx8hi Rolle's theorem?
@DhirajKumar-rx8hi
@DhirajKumar-rx8hi 2 жыл бұрын
@@pesilaratnayake162 yes
@lucasyoungers
@lucasyoungers 2 жыл бұрын
You know me and my boy Gauss came up with this devious theorem together
@drpeyam
@drpeyam 2 жыл бұрын
Hahahahaha
@jfcrow1
@jfcrow1 2 жыл бұрын
Even higher order derivative roots.
@AndDiracisHisProphet
@AndDiracisHisProphet 2 жыл бұрын
Just to be clear, this works with complex coefficients aswell?
@drpeyam
@drpeyam 2 жыл бұрын
Yep
@AndDiracisHisProphet
@AndDiracisHisProphet 2 жыл бұрын
@@drpeyam Thank you. This is the coolest thing in maths I have seen in quite some time. At least since the pi-is-equal-to-the-number-of-bumps-against-the-wall thing.
@drpeyam
@drpeyam 2 жыл бұрын
Agreeeeed
@jarikosonen4079
@jarikosonen4079 2 жыл бұрын
What happen with 4th or 5th degree case?
@drpeyam
@drpeyam 2 жыл бұрын
Same thing? Except that ellipse thing
@riccardoformenti4332
@riccardoformenti4332 2 жыл бұрын
So what if the roots of P are all on the real line? What’s the convex hull then?
@drpeyam
@drpeyam 2 жыл бұрын
The segment between the smallest root and the largest root
@riccardoformenti4332
@riccardoformenti4332 2 жыл бұрын
@@drpeyam cool
@jakolu
@jakolu 2 жыл бұрын
so if all 3 roots of the cubic are real then the roots of the derivative must also be real and between the largest and smallest roots of the cubic?
@drpeyam
@drpeyam 2 жыл бұрын
Exactly
@snakespeak
@snakespeak 2 жыл бұрын
@QuynhNguyen-cw6px
@QuynhNguyen-cw6px Жыл бұрын
Thay x =1 thì f(1)= 1-4+6-4#0; x=2 thì f(2)=8-16+12-4=0; f(x)= (x-2).g(x)
@mathadventuress
@mathadventuress 2 жыл бұрын
Out of curiosity does this work for non complex roots? Or is that just nonsense
@drpeyam
@drpeyam 2 жыл бұрын
There are only complex roots
@raminrasouli191
@raminrasouli191 2 жыл бұрын
👍
@royalfinest
@royalfinest 2 жыл бұрын
Is this P geometric or algebraic? Because VLT dont like it.
@drpeyam
@drpeyam 2 жыл бұрын
VLT?
@bandamkaromi
@bandamkaromi 2 жыл бұрын
I don't understand fully. ;-) But Good work.
@souravmallick7699
@souravmallick7699 2 жыл бұрын
Want to learn math till i can write from both hand actively 😄🤝
@ikramefa2019
@ikramefa2019 2 жыл бұрын
The théorème : Gauss Lucas
@henrymarkson3758
@henrymarkson3758 2 жыл бұрын
You coulda been a contender
@michaelempeigne3519
@michaelempeigne3519 2 жыл бұрын
i just noticed that this can only happen when the P ( x ) has only one real root.
@nullplan01
@nullplan01 2 жыл бұрын
Well, if it has three real roots, the convex hull is a section of the real axis, so the roots of the derivative are also in that section. So IOW, this proves that if all roots of a polynomial are real, then all roots of its derivative are also real.
@vishalmishra3046
@vishalmishra3046 2 жыл бұрын
The coefficients of P(x) look like the 4th row of Pascal's triangle [ 1 -4 6 -4 1 ]. Since x is not 0 so multiply x to get (x-1)^4 = 1. The 4 roots of unity are +/- 1 and +/- i => x = 2, 0, 1 +/- i (x is not 0 so discard that root). x = 2, 1+i and 1-i (No guessing of integer roots required).
@drpeyam
@drpeyam 2 жыл бұрын
You’re completely missing the point of the video omg
@harbalazzeh9129
@harbalazzeh9129 2 жыл бұрын
Holly
@deepak_mathphile
@deepak_mathphile 2 жыл бұрын
500th Viewer
@user-lr8od4uz1n
@user-lr8od4uz1n 2 жыл бұрын
I L.O.V.E U
@drpeyam
@drpeyam 2 жыл бұрын
It’s symmetric 😁
@karpsan2523
@karpsan2523 Жыл бұрын
American long division LMAO
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