Consider f and c below. f(x, y, z) = yzexzi + exzj + xyexzk,



c.r(t) = (t2 + 4)i + (t2 − 4)j + (t2 − 5t)k, 0 ≤ t ≤ 5 (a) find a function f such that f = ∇f.

Respuesta :

Answer:

[tex]f(x,y,z)=ye^{xz}+C[/tex]  

Step-by-step explanation:

We can write the given expression as :

[tex]\vec f(x,y,z)=yze^{xz}\,\vec\imath+e^{xz}\,\vec\jmath+xye^{xz}\,\vec k[/tex]

As given,   f = ∇f.

∇f = [tex]\dfrac{\partial f}{\partial x}i[/tex]  + [tex]\dfrac{\partial f}{\partial y}j[/tex]  +[tex]\dfrac{\partial f}{\partial z}k [/tex] 

We can write the partial derivative with respect to x, y and z.

[tex]\dfrac{\partial f}{\partial x}=yze^{xz}[/tex]       ___(Equation 1)

[tex]\dfrac{\partial f}{\partial y}=e^{xz}[/tex]               ______(Equation 2)

[tex]\dfrac{\partial f}{\partial z}=xye^{xz}[/tex]             ______(Equation 3)

Take equation 2 and integrate with respect to y,

[tex]\dfrac{\partial f}{\partial y}=e^{xz}[/tex]

[tex]f(x,y,z)=ye^{xz}+a(x,z)[/tex]           ----------Equation 4

Derivate both sides w.r.t x , we get :

[tex]\frac{d}{dx}(yze^{xz})=yze^{xz}+\dfrac{\partial a}{\partial x}[/tex]

or

[tex]\dfrac{\partial a}{\partial x}=0[/tex]

integrate

a(x,z)=b(z)

put in equation 4 ,

we get :

[tex]f(x,y,z)=ye^{xz}+b(z)[/tex]

take derivative wrt z

[tex]\frac{d}{dz} (ye^{xz}+b(z))\impliesxye^{xz}=xye^{xz}+\frac{db}{dz}[/tex]

we can take here:

[tex]\frac{db}{dz} = 0[/tex]

integrate:

[tex]\int\ {\frac{db}{dz} } \, =\int0[/tex]

b(z) = C

The function can be written as :

from equation 4 :

[tex]f(x,y,z)=ye^{xz}+C[/tex]  

Where C is a constant.