Puiseux expansions at branch points

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Find the first two terms in the expansion of yy in increasing powers of xx for the branches of the curve x3−3xy+y3=0x^{3}-3xy+y^{3} = 0 passing through the origin.

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Find the first two terms in the expansion of yy in increasing powers of xx for the branches of the curve y4−4y=xy^{4}-4y = x passing through the origin.

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Find the singular points of the equation y5+ax4−b2xy2=0y^{5}+ax^{4}-b^{2}xy^{2} = 0.

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Find the singular points of the equation 4(x−1)y5+2xy3−3x3y+x4=04(x-1)y^{5}+2xy^{3}-3x^{3}y+x^{4} = 0.

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Let z=az = a be a branch point of order nn for the function F(z)\mathcal{F}(z). Prove that the expression F(a+ζn)\mathcal{F}\left(a+\zeta^{n}\right) represents nn functions having the point ζ=0\zeta = 0 as an isolated singular point of single-valued character.

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Prove that if the function F(z)\mathcal{F}(z) has the point z=az = a as a branch point of order nn, then it can be represented in the form

F(z)=f(z−an) \mathcal{F}(z) = f(\sqrt[n]{z-a})

where the function f(w)f(w) has the point w=0w = 0 as an isolated singular point of single-valued character.

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Prove that a function F(z)\mathcal{F}(z) having at the point z=az = a an algebraic branch point of order nn can be represented in the form F(z)=f(z−an)\mathcal{F}(z) = f(\sqrt[n]{z-a}), where the function f(w)f(w) is regular at the point w=0w = 0 or has a pole there.

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Prove that a function F(z)\mathcal{F}(z) having at the point z=az = a an algebraic branch point of order nn can be represented in the form

F(z)=g0(z)+(z−a)1/ng1(z)+(z−a)2/ng2(z)+…++(z−a)(n−1)/ngn−1(z), \begin{aligned} \mathcal{F}(z) = & g_{0}(z)+(z-a)^{1 / n} g_{1}(z)+(z-a)^{2 / n} g_{2}(z)+\ldots + \\ & +(z-a)^{(n-1) / n} g_{n-1}(z), \end{aligned}

where the functions gk(z)g_{k}(z) are regular at the point z=az = a or have poles there.

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References

[ГюКу03] Гюнтер Н.М., Кузьмин Р.О. Сборник задач по высшей математике. 13-е изд., Издательство «Лань», 2003.
[ШПК15] Шабунин М.И., Половинкин Е.С., Карлов М.И. Сборник задач по теории функций комплексного переменного. 4-е изд., БИНОМ. Лаборатория знаний, 2015.