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Andrei [34K]
3 years ago
13

PLEASE PLEASE PLEASE HELP ME WITH THESE! Or I WILL FAIL!! PLEASE

Mathematics
1 answer:
Serga [27]3 years ago
6 0
First ones 40 and I’m not sure bout the second one but through process of elimination either always or never cause nothing in math is uncertain or non existent
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Let φ(x, y) = arctan (y/x) .
Alexandra [31]

Answer:

a) \large F(x,y)=(-\frac{y}{x^2+y^2},\frac{x}{x^2+y^2})

b) \large \mathbb{R}^2-\{(0,0)\}

c) the points of the form (x, -x) for x≠0

Step-by-step explanation:

a)

If φ(x, y) = arctan (y/x), the vector field F = ∇φ would be

\large F(x,y)=(\frac{\partial \phi}{\partial x},\frac{\partial \phi}{\partial y})

On one hand we have,

\large \frac{\partial \phi}{\partial x}=\frac{\partial arctan(y/x)}{\partial x}=\frac{-y/x^2}{1+(y/x)^2}=-\frac{y/x^2}{1+y^2/x^2}=\\\\=-\frac{y/x^2}{(x^2+y^2)/x^2}=-\frac{y}{x^2+y^2}

On the other hand,

\large \frac{\partial \phi}{\partial y}=\frac{\partial arctan(y/x)}{\partial y}=\frac{1/x}{1+(y/x)^2}=\frac{1/x}{1+y^2/x^2}=\\\\=\frac{1/x}{(x^2+y^2)/x^2}=\frac{x}{x^2+y^2}

So

\large F(x,y)=(-\frac{y}{x^2+y^2},\frac{x}{x^2+y^2})

b)

The domain of definition of F is  

\large \mathbb{R}^2-\{(0,0)\}

i.e., all the plane X-Y except the (0,0)

c)

Here we want to find all the points such that

\large (-\frac{y}{x^2+y^2},\frac{x}{x^2+y^2})=(k,k)

where k is a real number other than 0.

But this means

\large -\frac{y}{x^2+y^2}=\frac{x}{x^2+y^2}\Rightarrow y=-x

So, all the points in the line y = -x except (0,0) are parallel to the vector field F, that is, the points (x, -x) with x≠ 0

8 0
2 years ago
Bob Nale is the owner of Nale’s Quick Fill. Bob would like to estimate the mean number of gallons of gasoline sold to his custom
ira [324]

Answer:

a) The best estimator for the population mean is given by the sample mean \hat \mu = \bar X = 5.70

b) The 99% confidence interval would be given by (4.969;6.431)    

c) We are 99% confident that the true mean for th number of gallons of gasoline  sold to his customers is between 4.969 and 6.431.

Step-by-step explanation:

1) Previous concepts

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The margin of error is the range of values below and above the sample statistic in a confidence interval.

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

\bar X represent the sample mean for the sample  

\mu population mean (variable of interest)

\sigma=1.9 represent the population standard deviation

n=45 represent the sample size  

2) Part a

The best estimator for the population mean is given by the sample mean \hat \mu = \bar X = 5.70

3) Part b. Develop a 99 percent confidence interval for the population mean.

The confidence interval for the mean is given by the following formula:

\bar X \pm z_{\alpha/2}\frac{\sigma}{\sqrt{n}}   (1)

Since the Confidence is 0.95 or 95%, the value of \alpha=0.01 and \alpha/2 =0.005, and we can use excel, a calculator or a table to find the critical value. The excel command would be: "=-NORM.INV(0.005,0,1)".And we see that z_{\alpha/2}=2.58

Now we have everything in order to replace into formula (1):

5.7-2.58\frac{1.9}{\sqrt{45}}=4.969    

5.7+2.58\frac{1.9}{\sqrt{45}}=6.431

So on this case the 99% confidence interval would be given by (4.969;6.431)    

4) Part c. Interpret the meaning of part (b).

On this case we can say this: We are 99% confident that the true mean for th number of gallons of gasoline  sold to his customers is between 4.969 and 6.431.

4 0
3 years ago
Could any of y'all help me?
Scorpion4ik [409]
Start using calculator
5 0
3 years ago
For an art project, Kelvin cut a 4-foot piece of yarn into pieces. He then measured the length of each piece of yarn to the near
oksian1 [2.3K]

Answer:

I think answers is

D

label the x-axis "Pieces of Yarn," and label the y-axis "Length (inches

3 0
2 years ago
How to solve this problem
guapka [62]
2193 x 10(little 37) over 79

or

≈2.77595 x 10(little 38)

6 0
2 years ago
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