The problem asks to analyze the function $f(x, y) = e^x \cos y$.

AnalysisPartial DerivativesMultivariable CalculusLaplacianHarmonic Function
2025/4/25

1. Problem Description

The problem asks to analyze the function f(x,y)=excosyf(x, y) = e^x \cos y.

2. Solution Steps

There is no specific instruction. So let's analyze the function f(x,y)=excosyf(x, y) = e^x \cos y.
Partial derivative with respect to x:
fx=excosy\frac{\partial f}{\partial x} = e^x \cos y
Partial derivative with respect to y:
fy=exsiny\frac{\partial f}{\partial y} = -e^x \sin y
Second partial derivative with respect to x:
2fx2=excosy\frac{\partial^2 f}{\partial x^2} = e^x \cos y
Second partial derivative with respect to y:
2fy2=excosy\frac{\partial^2 f}{\partial y^2} = -e^x \cos y
Mixed partial derivative:
2fxy=exsiny\frac{\partial^2 f}{\partial x \partial y} = -e^x \sin y
2fyx=exsiny\frac{\partial^2 f}{\partial y \partial x} = -e^x \sin y
Laplacian:
2f=2fx2+2fy2=excosyexcosy=0\nabla^2 f = \frac{\partial^2 f}{\partial x^2} + \frac{\partial^2 f}{\partial y^2} = e^x \cos y - e^x \cos y = 0
The function is harmonic.

3. Final Answer

f(x,y)=excosyf(x, y) = e^x \cos y
fx=excosy\frac{\partial f}{\partial x} = e^x \cos y
fy=exsiny\frac{\partial f}{\partial y} = -e^x \sin y
2fx2=excosy\frac{\partial^2 f}{\partial x^2} = e^x \cos y
2fy2=excosy\frac{\partial^2 f}{\partial y^2} = -e^x \cos y
2fxy=exsiny\frac{\partial^2 f}{\partial x \partial y} = -e^x \sin y
2f=0\nabla^2 f = 0

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