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3 years ago

A circle has an area of 81pi square units. What is the diameter of the circle

Mathematics

2 answers:

Sonja [21]3 years ago

6 0

The diameter of the circle is 18 unit which is A. Hope it help!

Oksanka [162]3 years ago

6 0

Area of circle (Formula) = πr^2
<span>81π = πr^2 </span>
<span>r^2 = 81 </span>
<span>radius = 9 </span>
<span>
</span><span>Hope this helps!</span>

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Find the Fourier series of f on the given interval. f(x) = 1, ?7 < x < 0 1 + x, 0 ? x < 7

Zolol [24]

$f(x)=\begin{cases}1&\text{for }-7$

The Fourier series expansion of $f(x)$ is given by

$\dfrac{a_0}2+\displaystyle\sum_{n\ge1}a_n\cos\frac{n\pi x}7+\sum_{n\ge1}b_n\sin\frac{n\pi x}7$

where we have

$a_0=\displaystyle\frac17\int_{-7}^7f(x)\,\mathrm dx$
$a_0=\displaystyle\frac17\left(\int_{-7}^0\mathrm dx+\int_0^7(1+x)\,\mathrm dx\right)$
$a_0=\dfrac{7+\frac{63}2}7=\dfrac{11}2$

The coefficients of the cosine series are

$a_n=\displaystyle\frac17\int_{-7}^7f(x)\cos\dfrac{n\pi x}7\,\mathrm dx$
$a_n=\displaystyle\frac17\left(\int_{-7}^0\cos\frac{n\pi x}7\,\mathrm dx+\int_0^7(1+x)\cos\frac{n\pi x}7\,\mathrm dx\right)$
$a_n=\dfrac{9\sin n\pi}{n\pi}+\dfrac{7\cos n\pi-7}{n^2\pi^2}$
$a_n=\dfrac{7(-1)^n-7}{n^2\pi^2}$

When $n$ is even, the numerator vanishes, so we consider odd $n$ , i.e. $n=2k-1$ for $k\in\mathbb N$ , leaving us with

$a_n=a_{2k-1}=\dfrac{7(-1)-7}{(2k-1)^2\pi^2}=-\dfrac{14}{(2k-1)^2\pi^2}$

Meanwhile, the coefficients of the sine series are given by

$b_n=\displaystyle\frac17\int_{-7}^7f(x)\sin\dfrac{n\pi x}7\,\mathrm dx$
$b_n=\displaystyle\frac17\left(\int_{-7}^0\sin\dfrac{n\pi x}7\,\mathrm dx+\int_0^7(1+x)\sin\dfrac{n\pi x}7\,\mathrm dx\right)$
$b_n=-\dfrac{7\cos n\pi}{n\pi}+\dfrac{7\sin n\pi}{n^2\pi^2}$
$b_n=\dfrac{7(-1)^{n+1}}{n\pi}$

So the Fourier series expansion for $f(x)$ is

$f(x)\sim\dfrac{11}4-\dfrac{14}{\pi^2}\displaystyle\sum_{n\ge1}\frac1{(2n-1)^2}\cos\frac{(2n-1)\pi x}7+\frac7\pi\sum_{n\ge1}\frac{(-1)^{n+1}}n\sin\frac{n\pi x}7$

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2 years ago

Two men walk at rates 6miles per hour and 10 miles per hour. They started from the same place walking in opposite directions. In

Mamont248 [21]

Answer:

The answer is 50 hours

Step-by-step explanation:

4x = 200

Divide both sides by 4

x = 200 \div 4 = 50

so after 50 hours of walking, the men will be 200 miles apart.

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3 years ago

Evan is thinking of a number that contains the digit 2. The digit 2 in Evan's number has 10 times the value of the digit 2 in th

Len [333]

Answer:

200,000

Step-by-step explanation:

The number Evan could be thinking about is 200,000. I got this number because the value of the digit 2 in the number 328,907 is 20,000. Also, the number Evan is thinking about is 10 times the value of 20,000. So, I did 20,000 times 10 and got 200,000.

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2 years ago

Six hundred kilograms of tea were packed in 500 g packets. how many packets of tea were there?

Shtirlitz [24]

Answer:

1200 packets of tea

Step-by-step explanation:

Its because theres 1000 grams in 1kg so it would be 600000 grams and you would divided 600000 over 500 and get 1200

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2 years ago

Read 2 more answers

What is the area of georgina rounded to the nearest mile 59,424.77

AleksAgata [21]

<h2>Answer: </h2>

59,425 sq mi

<h2>Step-by-step explanation: </h2>

When you want to round to the units place, you look at the digit in the number that is in the place to the right of that: the tenths place. Here, that digit is 7, which is more than 4. Because that digit is more than 4, 1 is added to the units place and all the digits to the right of that are dropped.

This gives you 59,424 +1 = 59,425.

If the tenths digit were 4 or less, no change would be made to values in the units place or to the left of that. The tenths digit and digits to the right would be dropped.

... 59,424.3 ⇒ 59,424 . . . . . for example

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2 years ago