Восстановите аналитическую функцию f(z) по ее действительной части u = Re f(z) = -2xy - 2y?, при условии что f(0) = 0
思考
Clarifying the expression
The question asks to reconstruct the analytic function f(z) from its real part u = -2xy - 2y?. The expression might be unclear, possibly meaning u = -2xy - 2y^2.
Applying Cauchy-Riemann
I’m checking if u = -2xy - 2y^2 is harmonic by finding its partial derivatives. Then, I use the Cauchy-Riemann equations to determine v.
Pinpointing logical conflicts
I noticed that if g'(x) equals 2x + 4y, it contradicts the independence of g(x) from y. So, I re-evaluated and considered the Laplacian of u.
Evaluating harmonicity
Interestingly enough, I checked if u = -2xy - 2y^2 satisfied Laplace's equation. Since it didn't, I concluded that u isn't harmonic and can't be the real part of an analytic function.
Identifying the harmonic
Reassessing the derivatives, I confirmed that u = -2xy - 2y is indeed harmonic, with second partial derivatives summing to zero, maintaining the harmonic property.
Confirming consistency
I verified that u = -2xy - 2y aligns with the Cauchy-Riemann equations, leading to v = -y^2 + x^2 + 2x + C. The partial derivatives of v matched the calculations.
Confirming harmonicity
I verified that u = -2xy - 2y is harmonic, leading to v = -y^2 + x^2 + 2x + constant. This confirms the Cauchy-Riemann equations hold true.
Adjusting constant constraints
OK, I adjusted the constant C to ensure f(0) = 0, leading to f(z) = u + i v. Next, I restructured f in terms of z to align with the given conditions.
Crafting a polynomial
To find an analytical function, I’m working with a polynomial form, specifically f(z) = a z^2 + b z + c, aiming to match the real part.
Reworking the solution
I’m analyzing how to express f in terms of z by breaking down the real part u as (x+iy)^2 plus some additional terms. This leads me to a systematic approach.
Refining the derivative
I'm noticing that f'(z) breaks down to 2 (i x - y) plus other terms. This approach clarifies the structure and helps in aligning the result with the original conditions.
Redefining variables
I’m rewriting -2y using z. This approach shifts x and y to z and zˉ, ultimately expressing −2y as iz−izˉ.
Piecing together derivatives
I simplified f′(z) to 2i(z+1) by grouping and canceling terms, ensuring it aligns with the remaining terms.
Mapping out the derivative
I integrated 2i(z+1) to get f(z)=iz2+2iz+constant. Then, I re-expressed iz2 in terms of x and y to align with the real part.
Breaking down the real part
Interestingly enough, the real part of iz2 is −2xy, matching the given u=−2xy−2y2. This confirms the integration and manipulation were accurate.
Ensuring precision
I’m confirming that f(z)=iz2+2iz meets the requirement that f(0)=0, leading to the final expression.
Thought about восстановлении аналитической функции pendant 30 secondes
回答
Ниже приведено подробное решение на русском языке.
Шаг 1. Уточнение постановки задачи
Нам дана функция f(z), аналитическая в некоторой области (то есть голоморфная), и известна её действительная часть:
u(x,y)=ℜf(z)=−2xy−2y,
где z=x+iy. Требуется найти полную функцию
f(z)=u(x,y)+iv(x,y),
то есть найти и мнимую часть v(x,y), и при этом удовлетворить условию f(0)=0.
Чтобы ℜf(z) действительно являлась действительной частью аналитической функции, u(x,y) должна быть гармонической, и должны выполняться уравнения Коши–Римана.
Примечание. Судя по контексту, «−2xy−2y?» в условии, скорее всего, опечатка, и имеется в виду именно
u(x,y)=−2xy−2y.
Проверим, что это действительно гармоническая функция.
Шаг 2. Проверка гармоничности u(x,y)
Функция u(x,y) должна удовлетворять уравнению Лапласа: