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Slav-nsk
3 months ago
5

Determine whether each of the following functions is a solution of Laplace's equation uxx + uyy = 0. (Select all that apply.) u

= e^(−x) cos(y) − e^(−y) cos(x) u = sin(x) cosh(y) + cos(x) sinh(y)
Mathematics
1 answer:
PIT_PIT [12.4K]3 months ago
4 0

Answer with Step-by-step explanation:

We are given Laplace's equation:

u_{xx}+u_{yy}=0

We need to verify if the presented functions satisfy this equation.

A function solves Laplace's equation only if the sum of its second partial derivatives with respect to x and y equals zero.

For the first function:u=e^{-x}cosy-e^{-y}cosx

Compute the first derivative with respect to x:

u_x=-e^{-x}cosy+e^{-y}sinx

Then find the second derivative with respect to x:

u_{xx}=e^{-x}cosy+e^{-y}cosx

Next, derive with respect to y:

u_y=-e^{-x}siny+e^{-y}cosx

Then the second derivative with respect to y:

u_{yy}=-e^{-x}cosy-e^{-y}cosx

Substitute into Laplace's equation:

e^{-x}cosy+e^{-y}cosx-e^{-x}cosy-e^{-y}cosx=0

Therefore, the function satisfies Laplace's equation.

For the second function:u=sinx coshy+cosx sinhy

First partial derivative w.r.t x:

u_x=cosx coshy-sinx sinhy

Second derivative w.r.t x:

u_{xx}=-sin x coshy-cosxsinhy

First derivative w.r.t y:

u_y=sinx sinhy+cosx coshy

Second derivative w.r.t y:

u_{yy}=sinx coshy+cosx sinhy

After substituting, we have:

-sinx coshy-cosxsinhy+sinxcoshy+cosx sinhy=0

Hence, this function also solves Laplace's equation.

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2 months ago
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Required

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Read 2 more answers
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