If you put all the flowers together end to end, what would be the total length of all the flowers?

A rectangular field is to be enclosed by 400m of fencing. Use quadratic to

Marrrta [24]

Work:

First it's a rectangle so its area is equal to the product (multiplication) of both sides of the rectangle (dimensions). A = a x b = ab

NOW: knowing the the circumference or perimeter is equal to 400m, we can say that P = 400 = 2(a+b) = 2a + 2b since the given polynom is rectangle. 2a + 2b = 400 <==> 2a = 400 - 2b <==> a = 200 - b.

We gave an expression of a in function of b. Now we can replace the variable a by 200 - b in the first expression of the area.

A = ab = (200-b)b = 200b-b^2 = -b^2 + 200b

A is now a quadratic equation. We note A(b) the epression -b^2 +200b so:

A(b) = -b^2 +200b

We can already see that A is a quadratic equation of the form:

ax^2 + b + c. The a coefficient is negative which will lead to closed parabola when looking from the top. Now we need to find the maximum of the function by using the derivatives:

A(b) = -b^2 +200b <==> A'(b) = -2b + 200b

and -2b + 200b = 0 <==> b = 100;

So the derivative function crosses the x-axis at (100; 0).

So is increasing over ]-∞; 100] and decreasing over [100; ∞[.

We obtain a maxima on (100; x) with A. To find it we need to replace 100 by b in the function A.

A(b) = -b^2 + 200b

<==> A(100) = -100^2 + 200 x 100 = - 10000 + 20000 = 10000

Now let's find a: if b = 100 what equals a ?

We know that ab = 10000 <==> 100a = 10000 <==> a = 100;

And we verify that ab = 100 x 100 = 10000.

The rectangle needs to be a square to reach the maximum area of 10000m^2 or also 0.01 km^2.

Q.E.D.

6 0

2 years ago

And this question please?

defon

Answer:

this would be 5

Step-by-step explanation:

beacuse it has a different answer every time

6 0

3 years ago

In 2010, the Census Bureau estimated the proportion of all Americans who own their homes to be 0.669. An urban economist wants t

Alexxandr [17]

Answer:

i)

Sample size making use of the Census Bureau: 1,499 American adults.

Sample size without making use of the Census Bureau: 1,692 American adults

ii)

71

Step-by-step explanation:

i)

The sample size n in Simple Random Sampling is given by

$\bf n=\frac{z^2p(1-p)}{e^2}$

where

z = 1.645 is the critical value for a 90% confidence level (*) 

p= 0.669 is the population proportion given by the Census

e = 0.02 is the margin of error

so

$\bf n=\frac{(1.645)^2*0.669*0.331}{0.02^2}=1,498.05\approx 1,499$

rounded up to the nearest integer.

(*)This is a point z such that the area under the Normal curve N(0,1) 1nside the interval [-z, z] equals 90% = 0.9

It can be obtained with tables or in Excel or OpenOffice Calc with

NORMSINV(0.95)

If she ignores the Census estimate, the she has to take the largest sample possible that meets the requirements.

Let's show it is obtained when p = 0.5

As we said, the sample size n is

$\bf n=\frac{z^2p(1-p)}{e^2}$

where

e = 0.02 is the error proportion

z = 1.645

hence

$\bf n=\frac{(1.645)^2p(1-p)}{(0.02)^2}=6765.0625p(1-p)=6765.0625p-6765.0625p^2$

taking the derivative with respect to p, we get

n'(p)=6765.0625-2*6765.0625p

and

n'(p) = 0 when p=0.5

By taking the second derivative we see n''(p)<0, so p=0.5 is a maximum of n

This means that if we set p=0.5, we get the maximum sample size for the confidence level required for the proportion error 0.02

Replacing p with 0.5 in the formula for the sample size we get

$\bf n=6765.0625*0.5-6765.0625(0.5)^2=1691.27\approx 1,692$

rounded to the nearest integer.

ii)

When we do not have a proportion but a variable whose approximate standard deviation s is known, then the sample size n in Simple Random Sampling is given by

$\bf n=\frac{z^2s^2}{e^2}$