I need help finding this

The plane x + y + z = 12 intersects paraboloid z = x^2 + y^2 in an ellipse.(a) Find the highest and the lowest points on the ell

emmasim [6.3K]

Answer:

a)

Highest (-3,-3)

Lowest (2,2)

b)

Farthest (-3,-3)

Closest (2,2)

Step-by-step explanation:

To solve this problem we will be using Lagrange multipliers.

a)

Let us find out first the restriction, which is the projection of the intersection on the XY-plane.

From x+y+z=12 we get z=12-x-y and replace this in the equation of the paraboloid:

$\bf 12-x-y=x^2+y^2\Rightarrow x^2+y^2+x+y=12$

completing the squares:

$\bf x^2+y^2+x+y=12\Rightarrow (x+1/2)^2-1/4+(y+1/2)^2-1/4=12\Rightarrow\\\\\Rightarrow (x+1/2)^2+(y+1/2)^2=12+1/2\Rightarrow (x+1/2)^2+(y+1/2)^2=25/2$

and we want the maximum and minimum of the paraboloid when (x,y) varies on the circumference we just found. That is, we want the maximum and minimum of

$\bf f(x,y)=x^2+y^2$

subject to the constraint

$\bf g(x,y)=(x+1/2)^2+(y+1/2)^2-25/2=0$

Now we have

$\bf \nabla f=(\displaystyle\frac{\partial f}{\partial x},\displaystyle\frac{\partial f}{\partial y})=(2x,2y)\\\\\nabla g=(\displaystyle\frac{\partial g}{\partial x},\displaystyle\frac{\partial g}{\partial y})=(2x+1,2y+1)$

Let $\bf \lambda$ be the Lagrange multiplier.

The maximum and minimum must occur at points where

$\bf \nabla f=\lambda\nabla g$

that is,

$\bf (2x,2y)=\lambda(2x+1,2y+1)\Rightarrow 2x=\lambda (2x+1)\;,2y=\lambda (2y+1)$

we can assume (x,y)≠ (-1/2, -1/2) since that point is not in the restriction, so

$\bf \lambda=\displaystyle\frac{2x}{(2x+1)} \;,\lambda=\displaystyle\frac{2y}{(2y+1)}\Rightarrow \displaystyle\frac{2x}{(2x+1)}=\displaystyle\frac{2y}{(2y+1)}\Rightarrow\\\\\Rightarrow 2x(2y+1)=2y(2x+1)\Rightarrow 4xy+2x=4xy+2y\Rightarrow\\\\\Rightarrow x=y$

Replacing in the constraint

$\bf (x+1/2)^2+(x+1/2)^2-25/2=0\Rightarrow (x+1/2)^2=25/4\Rightarrow\\\\\Rightarrow |x+1/2|=5/2$

from this we get

and the candidates for maximum and minimum are (2,2) and (-3,-3).

Replacing these values in f, we see that

f(-3,-3) = 9+9 = 18 is the maximum and

f(2,2) = 4+4 = 8 is the minimum

b)

Since the square of the distance from any given point (x,y) on the paraboloid to (0,0) is f(x,y) itself, the maximum and minimum of the distance are reached at the points we just found.

We have then,

(-3,-3) is the farthest from the origin

(2,2) is the closest to the origin.

3 0

3 years ago

How do you get a34 from a=-11+7n

marissa [1.9K]

Answer:

Step-by-step explanation:

34=-11+7A

We move all terms to the left:

34-(-11+7A)=0

We add all the numbers together, and all the variables

-(7A-11)+34=0

We get rid of parentheses

-7A+11+34=0

We add all the numbers together, and all the variables

-7A+45=0

We move all terms containing A to the left, all other terms to the right

-7A=-45

A=-45/-7

A=6+3/7

6 0

3 years ago

Hezekiel runs 1000 m at a rateof 3 minutes per km. how long does he take to run 500 m

lana66690 [7]

Step-by-step explanation:

1 km = 1000 m

(hence the term "kilo" which means 1000).

so. he runs 1000 m at the rate of 3 minutes per km, that means 3 minutes per 1000 m.

now, we can see the solution already with our eyes.

but let's do it formally :

the rate or ratio between time and distance must be the same for the same speed.

so,

3 min / 1000 m = x min / 500 m

500 m × 3 min / 1000 m = x min

1/2 × 3 min = x min

3/2 = 1.5 min = x min

so, it takes him 1.5 minutes (90 seconds) to run 500 m.

3 0

2 years ago

8,000 customers eating lunch, 1,600 ordered Pepsi. what percentage ordered Pepsi

geniusboy [140]

1,600 of 8,000 = 20%

4 0

3 years ago

An intelligence test that has a maximum completion time of 45 minutes was recently administered to a group of 9 people. Their re

Ede4ka [16]

Answer:

a) $\bar X=39.9$

b) Median =40

c) Bimodal distribution 40,45 with a frequency of 2 for each one

Step-by-step explanation:

Part a

The statistical mean refers "to the mean or average that is used to derive the central tendency of the data in question. It is determined by adding all the data points in a population and then dividing the total by the number of points". And is defined:

$\bar X =\frac{\sum_{i=1}^n x_i}{n}$

And for this case if we apply this formula we got:

$\bar X =\frac{45+40+42+39+44+40+45+33+21}{9}=39.9$

Part b

The median is a "measure of central tendency. To find the median, we arrange the observations in order from smallest to largest value. And we have two possible cases:

1) If there is an odd number of observations, the median is the middle value. 2) If there is an even number of observations, the median is the average of the two middle values."

So if we order the dataset we got:

31,33,39,40,40,42,44,45,45

Since we have an odd number of observation n=9, the median would be just the middle value on position 5 and for this case Median =40

Part c

The mode of a set of data values is the value that appears most often. As a set of data can have more than one mode, the mode does not necessarily indicate the centre of a data set.

For this case we have a bimodal distribution and the corresponding values are 40 and 45 with a frequency of 2 for each one.

8 0

3 years ago

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