Increment of the argument along a curve

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Let ff be the analytic function defined in the disk Δ={z:∣z−4∣<4}\Delta = \left\{ z : \left|z-4\right| < 4\right\} so that f(z)=z1/3(z+1)1/2f(z) = z^{1/3}(z+1)^{1/2} in Δ\Delta and f(x)f(x) is positive for 0<x<80 < x < 8. An analytic function gg in Δ\Delta is obtained from ff by analytic continuation along the path starting and ending at z=4z = 4 (see Fig. 5.2). Express gg in terms of ff.

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Trace how the argument of the quantity x(x−1)x(x-1) changes as xx traces, counterclockwise, a closed curve enclosing the points 00 and 11.

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Study how the arguments of the quantities x\sqrt{x}, x−1\sqrt{x-1}, and x(x−1)\sqrt{x(x-1)} change as xx traces the same contour as in problem 2480 (a closed curve traversed counterclockwise and enclosing the points 00 and 11).

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How does the function u=(z−a)α(z−b)βu=(z-a)^{\alpha }(z-b)^{\beta } change, for real α\alpha and β\beta, if zz traces a closed contour going counterclockwise around the points aa and bb?

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The same question for the function u=(z−a)αln⁡(z−a)u=(z-a)^{\alpha }\ln (z-a) and a contour going counterclockwise around the point aa.

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Remark.
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The question concerns how the function u=(z−a)αln⁡(z−a)u=(z-a)^{\alpha }\ln (z-a) changes, for real α\alpha, if zz traces a closed contour going counterclockwise around the point aa (by analogy with problem 2482).

Study the change in arg⁡z−an\arg \sqrt[n]{z-a} as the point zz traces a simple closed contour going around the point z=az = a in the positive direction.

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Study the change in the function 1−z2\sqrt{1-z^{2}} as the point zz traces a simple closed contour of one of three kinds:

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(a)

going around one of the points z=±1z = \pm 1,

(b)

going around both of these points,

(c)

leaving these points outside the contour.

Find the increment of the argument of the function z(⋅)∈C1[0,1]z(\cdot ) \in C^{1}[0,1] on the segment [0,1][0,1], given in the form z(t)=x(t)+iy(t)z(t) = x(t)+i y(t), where

x(t)=4cos⁡(π2t)−3,y(t)=3sin⁡(π2t) x(t) = 4 \cos \left(\frac{\pi }{2} t\right)-3, \quad y(t) = 3 \sin \left(\frac{\pi }{2} t\right)
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Find the increment of the argument of the function z(⋅)∈C1[0,1]z(\cdot ) \in C^{1}[0,1] on the segment [0,1][0,1], given in the form z(t)=x(t)+iy(t)z(t) = x(t)+i y(t), where

x(t)=(2+t)sin⁡4πt,y(t)=(1+t)cos⁡4πt+32 x(t) = (2+t) \sin 4 \pi t, \quad y(t) = (1+t) \cos 4 \pi t+\frac{3}{2}
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Compute the increment of the argument of the function z2+1z^{2}+1 along the oriented curve γ\gamma, given in the form z(t)=x(t)+iy(t)z(t) = x(t)+i y(t), where

x(t)=5cos⁡t,y(t)=2sin⁡t,t∈[0,π2]. x(t) = 5 \cos t, \quad y(t) = 2 \sin t, \quad t \in \left[0, \frac{\pi }{2}\right].
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Compute the increment of the argument of the function 1z2+2z\frac{1}{z^{2}+2 z} along the oriented curve γ\gamma, given in the form z(t)=x(t)+iy(t)z(t) = x(t)+i y(t), where

x(t)=3sin⁡t,y(t)=2cos⁡t,t∈[0,π2] x(t) = 3 \sin t, \quad y(t) = 2 \cos t, \quad t \in \left[0, \frac{\pi }{2}\right]
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Compute the increment of the argument of the function z2+1z2−4\frac{z^{2}+1}{z^{2}-4} along the oriented curve γ\gamma, given in the form z(t)=x(t)+iy(t)z(t) = x(t)+i y(t), where

x(t)=cos⁡t,y(t)=2sin⁡t,t∈[π2,32π]. x(t) = \cos t, \quad y(t) = 2 \sin t, \quad t \in \left[\frac{\pi }{2}, \frac{3}{2} \pi \right].
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Compute the increment of the argument of the function tg⁡zz\frac{\operatorname {tg} z}{z} along the oriented closed curve given by the equation

∣x∣1/2+∣y∣1/2=21/2, \left|x\right|^{1 / 2}+\left|y\right|^{1 / 2} = 2^{1 / 2},

when it is traversed once counterclockwise.

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Compute the increment of the argument of the function ch2zz\frac{\mathrm{ch}^{2} z}{z} along the oriented closed curve given by the equation ∣x∣+∣y∣=3\left|x\right|+\left|y\right| = 3, when it is traversed once clockwise.

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Prove the equality

Δγarg⁡z=Δγarg⁡(z−1) \Delta _{\gamma } \arg z = \Delta _{\gamma } \arg (z-1)

for any simple piecewise-smooth closed curve γ\gamma such that the domain bounded by the curve γ\gamma contains the segment [0,1][0,1].

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References

[CJP+11] Chen J., Jiang G., Pan Y., Qin T., Tong Y., Wu Q., Xu S., Li T. Problems and Solutions in Mathematics. 2nd ed., World Scientific, 2011.
[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.