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Find the directional derivative of f(x,y,z)=z3−x2yf(x,y,z)=z3−x2y at the point (−5,5,2)(−5,5,2) in the direction of the vector v

olga_2 [115]

We are given

$f=z^3 -x^2y$

Firstly, we can find gradient

so, we will find partial derivatives

$f_x=0 -2xy$

$f_x=-2xy$

$f_y=0 -x^2$

$f_y=-x^2$

$f_z=3z^2$

now, we can plug point (-5,5,2)

$f_x=-2*-5*5=50$

$f_y=-(-5)^2=-25$

$f_z=3(2)^2=12$

so, gradient will be

$gradf=(50,-25,12)$

now, we are given that

it is in direction of v=⟨−3,2,−4⟩

so, we will find it's unit vector

$|v|=\sqrt{(-3)^2+(2)^2+(-4)^2}$

$|v|=\sqrt{29}$

now, we can find unit vector

$v'=(\frac{-3}{\sqrt{29} } , \frac{2}{\sqrt{29} } , \frac{-4}{\sqrt{29} })$

now, we can find dot product to find direction of the vector

$dir=(gradf) \cdot (v')$

now, we can plug values

$dir=(50,-25,12) \cdot (\frac{-3}{\sqrt{29} } , \frac{2}{\sqrt{29} } , \frac{-4}{\sqrt{29} })$

$dir=(-\frac{150}{\sqrt{29} } - \frac{50}{\sqrt{29} } - \frac{48}{\sqrt{29} })$

$dir=-\frac{248\sqrt{29}}{29}$ .............Answer

7 0

3 years ago

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An electrician charges $40 dollars to come to your house. She also charges $55 for each hour that she works. The electricion cha

Alexxx [7]

Answer:

your question doesn't make sense if an electrician came to your house it would cost $40 then $55 dollars per hour but there is no way that you can solve that (40+(55•2)=150+55=205 which is already over $190 dollars

3 0

3 years ago

Casandra is training for 10 mile race. On the first day of training she runs 4 miles, each day after that she adds on 0.5 mile.

Naddik [55]

On day no 9, because to increase her mileage by 4 to reach 8 it will take her 4/0.5=8 days plus day 1 where she ran just 4 miles.

8 0

3 years ago

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Question is: Solve -7(x+6)=4(x+6)

Alina [70]

$\huge\boxed{x=-6}$

Hey there! Our goal here is to isolate the variable on one side of the equation.

$\begin{aligned}-7(x+6)&=4(x+6)&&\smash{\Big|}&&\textsf{Start with the original equation.}\\-7x+(-7)(6)&=4x+4(6)&&\smash{\Big|}&&\textsf{Distribute.}\\-7x-42&=4x+24&&\smash{\Big|}&&\textsf{Multiply.}\\-7x-4x&=24+42&&\smash{\Big|}&&\textsf{Move the terms.}\\-11x&=66&&\smash{\Big|}&&\textsf{Combine like terms.}\\x&=\boxed{-6}&&\smash{\Big|}&&\textsf{Divide both sides by $-11$.}\end{aligned}$