What are the intercept(s) of ƒ(x) = x2?

If f(x, y, z) = x sin(yz), (a) find the gradient of f and (b) find the directional derivative of f at (2, 4, 0) in the direction

valentina_108 [34]

Answer:

a) $\nabla f(x,y,z) = \sin{yz}\mathbf{i} + xz\cos{yz}\mathbf{j} + xy \cos{yz}\mathbf{k}$ .

b) $Du_{f}(2,4,0) = -\frac{8}{\sqrt{11}}$

Step-by-step explanation:

Given a function $f(x,y,z)$ , this function has the following gradient:

$\nabla f(x,y,z) = f_{x}(x,y,z)\mathbf{i} + f_{y}(x,y,z)\mathbf{j} + f_{z}(x,y,z)\mathbf{k}$ .

(a) find the gradient of f

We have that $f(x,y,z) = x\sin{yz}$ . So

$f_{x}(x,y,z) = \sin{yz}$

$f_{y}(x,y,z) = xz\cos{yz}$

$f_{z}(x,y,z) = xy \cos{yz}$ .

$\nabla f(x,y,z) = f_{x}(x,y,z)\mathbf{i} + f_{y}(x,y,z)\mathbf{j} + f_{z}(x,y,z)\mathbf{k}$ .

$\nabla f(x,y,z) = \sin{yz}\mathbf{i} + xz\cos{yz}\mathbf{j} + xy \cos{yz}\mathbf{k}$

(b) find the directional derivative of f at (2, 4, 0) in the direction of v = i + 3j − k.

The directional derivate is the scalar product between the gradient at (2,4,0) and the unit vector of v.

We have that:

$\nabla f(x,y,z) = \sin{yz}\mathbf{i} + xz\cos{yz}\mathbf{j} + xy \cos{yz}\mathbf{k}$

$\nabla f(2,4,0) = \sin{0}\mathbf{i} + 0\cos{0}\mathbf{j} + 8 \cos{0}\mathbf{k}$ .

$\nabla f(2,4,0) = 0i+0j+8k=(0,0,8)$

The vector is $v = i + 3j - k = (1,3,-1)$

To use v as an unitary vector, we divide each component of v by the norm of v.

$|v| = \sqrt{1^{2} + 3^{2} + (-1)^{2}} = \sqrt{11}$

So

$v_{u} = (\frac{1}{\sqrt{11}}, \frac{3}{\sqrt{11}}, \frac{-1}{\sqrt{11}})$

Now, we can calculate the scalar product that is the directional derivative.

$Du_{f}(2,4,0) = (0,0,8).(\frac{1}{\sqrt{11}}, \frac{3}{\sqrt{11}}, \frac{-1}{\sqrt{11}}) = -\frac{8}{\sqrt{11}}$

6 0

3 years ago

Kelly plans to put her graduation money into an account and leave it there for 4 years while she goes to college. she recieves $

Firlakuza [10]

Answer:

C) $877.50

Step-by-step explanation:

Time t = 4 years

Principal, p = $750

rate, r = 4.25% = 0.0425

Amount that will be in her account in four years =

Simple interest (prt/100) + principal

750 * 4.25* 4 / 100 + 750

127.5 + 750

= $877.50

7 0

3 years ago

$800 is deposited in an account

Sergeeva-Olga [200]

Answer:

The balance after four years is $1129.27

Step-by-step explanation:

The formula for compound interest, including principal sum, is $A=P(1+\frac{r}{n})^{nt}$

A = the future value of the investment/loan, including interest
P = the principal investment amount (the initial deposit or loan amount)
r = the annual interest rate (decimal)
n = the number of times that interest is compounded per unit t
t = the time the money is invested or borrowed for

∵ $800 is deposited in an account

∴ P = 800

∵ The account pays 9% annual interest

∴ r = 9% = 9 ÷ 100 = 0.09

∵ The interest is compounded annually

∴ n = 1

∵ The time is 4 years

∴ t = 4

- Substitute the values of P, r, n, and t in the formula above

∵ $A=800(1+\frac{0.09}{1})^{(1)(4)}$

∴ $A=800(1.09)^{4}$

∴ A = 1129.265

∴ The balance after four years is $1129.27

8 0

3 years ago

The volume of a cube is 441cm3.<br> Work out the length of its side rounded to 1 DP.

Rainbow [258]

Answer:

volume of cube=441cm³

l³=441cm³

l=

$\sqrt[3]{441}$

length=7.6cm

3 0

3 years ago

Is there another way to write JK? Why or why not?

daser333 [38]

Answer:

What do u mean

. I'm confused

4 0

3 years ago

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