What is the length of AC

Find the area of the helicoid (or spiral ramp) with vector equation r(u, v) = ucos(v) i + usin(v) j + v k, 0 ≤ u ≤ 1, 0 ≤ v ≤ 9π

Natasha2012 [34]

Let $H$ denote the helicoid parameterized by

$\mathbb r(u,v)=u\cos v\,\mathbf i+u\sin v\,\mathbf j+v\,\mathbf k$

for $0\le u\le1$ and $0\le v\le9\pi$ . The surface area is given by the surface integral,

$\displaystyle\iint_H\mathrm dS=\iint_H\|\mathbf r_u\times\mathbf r_v\|\,\mathrm du\,\mathrm dv$

We have

$\mathbf r_u=\dfrac{\partial\mathbf r(u,v)}{\partial u}=\cos v\,\mathbf i+\sin v\,\mathbf j$
$\mathbf r_v=\dfrac{\partial\mathbf r(u,v)}{\partial v}=-u\sin v\,\mathbf i+u\cos v\,\mathbf j+\mathbf k$
$\implies\mathbf r_u\times\mathbf r_v=\sin v\,\mathbf i-\cos v\,\mathbf j+u\,\mathbf k$
$\implies\|\mathbf r_u\times\mathbf r_v\|=\sqrt{1+u^2}$

So the area of $H$ is

$\displaystyle\iint_H\mathrm dS=\int_{v=0}^{v=9\pi}\int_{u=0}^{u=1}\sqrt{1+u^2}\,\mathrm du\,\mathrm dv$
$=\dfrac{9(\sqrt2+\sinh^{-1}(1))\pi}2$

5 0

3 years ago

How to solve from 86 books to 150 books

True [87]

Hey!

I assume you're talking about percentage. What was the percentage increase from 86 books to 150.

Using the formula to find percentage increase, we will solve this:

{(86 - 150) / 86} × 100 = 74.42

So, the percent increase from 86 books to 150 is 74.42%

5 0

4 years ago

Jeffrey is a kickboxing instructor who will be teaching classes at a local gym. To get certified

tatyana61 [14]

If Jeffrey takes 50 classes in his first month as an instructor, he will earn back the amount he spent on certification.

Step-by-step explanation:

Amount spent on certification = $200

Base salary = $50

Payment per class = $3

Let, x be the number of classes.

J(x) = 50+3x

He needs to earn $200 dollars in first month, therefore,

50+3x=200

$3x=200-50\\3x=150$

Dividing both sides by 3

$\frac{3x}{3}=\frac{150}{3}\\x=50$

If Jeffrey takes 50 classes in his first month as an instructor, he will earn back the amount he spent on certification.

Keywords: function, linear equation

Learn more about functions at:

#LearnwithBrainly

7 0

3 years ago

Can someone help me with this?

skelet666 [1.2K]

The answers are C, C, B

6 0

3 years ago

Select the equivalent expression.

Free_Kalibri [48]

Answer:

$\frac{7^{15}}{3^{30}}$

Step-by-step explanation:

The given expression is:

$(\frac{3^{-6}}{7^{-3}})^{5}$

Moving the expression to the other side in the fraction changes its sign to opposite. A numerator with negative exponent, when written in denominator will have the positive exponent. Using this rule, we can write:

$(\frac{3^{-6}}{7^{-3}})^{5}\\\\ = (\frac{7^{3}}{3^{6}} )^{5}$

The exponent 5 can be distributed to both numerator and denominator as shown:

$(\frac{7^{3}}{3^{6}} )^{5}\\\\ = \frac{(7^{3})^{5}}{(3^{6})^{5}}$

The power of a power can be written as a product. i.e.

$\frac{(7^{3})^{5}}{(3^{6})^{5}}\\\\ =\frac{7^{15}}{3^{30}}$

So, the expression similar to the given expression and with positive exponents is: $\frac{7^{15}}{3^{30}}$

6 0

3 years ago

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