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Dima020 [189]
3 years ago
13

What is the radius of a circle whose equation is x2 + y2 + 8x – 6y + 21 = 0? units

Mathematics
2 answers:
Artemon [7]3 years ago
5 0

Answer:

2 units

Step-by-step explanation:

on edg

weqwewe [10]3 years ago
4 0

To answer this, use "completing the square."

x2 + y2 + 8x – 6y + 21 = 0 becomes

x^2 + 8x + 16 - 16 + y^2 - 6y + 9 - 9 + 21 = 0

 (x + 4)^2       -16     + (y - 3)^2     + 12 = 0

or   (x + 4)^2      + (y - 3)^2   = 4

Since 4 = r^2, r = 2 units, and the center is at (-4, 3)

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A simple random sample of size nequals81 is obtained from a population with mu equals 83 and sigma equals 27. ​(a) Describe the
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Answer:

a) \bar X \sim N (\mu, \frac{\sigma}{\sqrt{n}})

With:

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\sigma_{\bar X}=\frac{27}{\sqrt{81}}= 3

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Step-by-step explanation:

For this case we know the following propoertis for the random variable X

\mu = 83, \sigma = 27

We select a sample size of n = 81

Part a

Since the sample size is large enough we can use the central limit distribution and the distribution for the sampel mean on this case would be:

\bar X \sim N (\mu, \frac{\sigma}{\sqrt{n}})

With:

\mu_{\bar X}= 83

\sigma_{\bar X}=\frac{27}{\sqrt{81}}= 3

Part b

We want this probability:

P(\bar X>89)

We can use the z score formula given by:

z = \frac{\bar X -\mu}{\frac{\sigma}{\sqrt{n}}}

And if we find the z score for 89 we got:

z= \frac{89-83}{\frac{27}{\sqrt{81}}}= 2

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Part c

P(\bar X

We can use the z score formula given by:

z = \frac{\bar X -\mu}{\frac{\sigma}{\sqrt{n}}}

And if we find the z score for 75.65 we got:

z= \frac{75.65-83}{\frac{27}{\sqrt{81}}}= -2.45

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Part d

We want this probability:

P(79.4 < \bar X < 89.3)

We find the z scores:

z= \frac{89.3-83}{\frac{27}{\sqrt{81}}}= 2.1

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