Melody

921 Questions
34315 Answers

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Mathigon website

I just discovered a site called mathigon

https://mathigon.org/dashboard
और पढ़ें ..

Melody 2 Apr 2022

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Reporting problems.

There are a number of people having problems at the moment.
If you lodge an error can you please give all relevant information that you can think of.
Where you are in the world - the city or the country - is often very important information. और पढ़ें ..

Melody 16 Mar 2022

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How to make an empty rectangle in Latex

I just worked out how to make an empty box of various horizonal size easily in LaTex.
This is not a recommended method, but other methods that I have tried here have not worked.
This coding is really simple. Just put letters inside और पढ़ें ..

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Melody 15 Mar 2022

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856

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HAPPY ANNIVERSARY CHRIS! (CPhill)

I just realized that you became a member here exactly 8 years ago today!

It has been great to have you here all that time

और पढ़ें ..

विषय से परेे

Melody 13 Mar 2022

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WELCOME BACK CPHILL !

Melody 11 Feb 2022

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Very interesting question. No high level maths required.

This question was posted a couple of days ago.
https://web2.0calc.com/questions/geometry_73561

I think it is really interesting. It looks much more difficult than it really needs to be. और पढ़ें ..

Melody 1 Feb 2022

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Members have a better experience. Their questions get more attention.

Almost everyone is posting as a guest.
If you post as a member your questions will have a far greater chance of a timely and helpful response.
If you are a genuine learner and interact with us, you will become known and answerers will do और पढ़ें ..

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Melody 9 Jan 2022

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HAPPY BIRTHDAY CHRIS!

और पढ़ें ..

Melody 20 Des 2021

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Some guidelines for question askers.

Please note:
1) Ask only one question per post.
2) When asking a question talk about what you have tried for yourself. Then people will take you more seriously and will be more able and willing to help.
3) If you get an answer और पढ़ें ..

विषय से परेे

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Melody 4 Nov 2021

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Remeniscing - a little historical humour.

I just found this old post that some of you, who have been around for a while, might find amusing.

https://web2.0calc.com/questions/look-at-the-new-leader-board

विषय से परेे

Melody 29 Okt 2021

+118689

0

You would have to convert all the units to mm before you multiply and the answer would be in mm ³ NOT mm. It would be a volume.

Melody24 Okt 2013

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Melody24 Okt 2013

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Hi I have a cone of 100m radius and 17m height made out of a fabric of 0.01 millimeters.
I need to calculate the volume this takes when folded.
I have done this 2 different ways and got 2 different answers. I didn't expect the answers to be identical but they are too different.
Maybe someone in the forum can spot the fallacy.

method 1 - I think that this is the intended, more usual solution.

I have assumed that the cone is open. If it is not open then you will need to add the area of the circular base before you multiply by the thickness.

The material is 0.01/1000 = 0.00001m thick
If the radius of the cone is 100m and the perpendicular height is 17m
then the slant height is sqr(100 ² + 17 ²]) = sqr( 10289) = approx 101.435 metres

Surface Area of the cone = slant height * radius * pi = 101.435 * 100 * pi = approx 31,866.653 m ²

Volume = area * thickness = 31,866.653 * 0.00001 = approx 0.32 m ³

It think it would have to be very well vaccuum packed to get anywhere near this small but using this method this is about how much space the material would take up.

You may like to look at the web page below.
http://www.wikihow.com/Find-the-Surface-Area-of-Cones

Method 2

This time I found the internal volume of the pyramid and subtracted it from the external volume
I took the internal radius to be 100m and the external radius to be 100.00001m

V = (1/3) * pi * r ² * h

Internal volume
= (1/3) * pi * 100 ² * 17
=178023.5837m ³

External volume
=(1/3) * pi * 100.00001 ² * 17
=(1/3) * pi * 10000.0020000001 * 17
=178023.6190814

Difference= 178023.6190814 - 178023.5837 = 3.53 * 10 ^-2 = 0.035 m ³

I did try letting the external radius be 100m but it made very little difference to the answer.

So the first more conventional method gives a volume of 0.32m ³ and the second method gives a volume of 0.035m ³

I expected the two answers to be almost identical. Can someone see where my logic or my calculations are at fault and explain it to me please.

Melody23 Okt 2013

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e=0.5*c*v^2 => 2e = cv^2 => c = 2e/ v^2

Melody23 Okt 2013

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(10^10)^10,000,000 = 10 ^ 100,000,000
this is 1 followed by one hundred million zeros.

Melody23 Okt 2013

+118689

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if x= 2 is a solution of a equation x2 - 7x + k = 0 what is k

Just substitute 2 in for x in the equation

2 ² - 7* 2 + k=0

4 - 14 + k = 0

-10 +k = 0

k =10

Melody23 Okt 2013

+118689

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length^3 = 512

so length = cube root of 512

Melody23 Okt 2013

+118689

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x ²+9x+6=0

You have to use the quadratic formula to solve this problem

x = -b+- sqr(b^2-4ac) ALL over 2a
where a=1 b=9 and c=6

Melody23 Okt 2013

+118689

0

Do you mean

9 ^-3 /2 OR 9 ^(-3/2)

I'll solve 9 ^(-3/2)

= 9 ^{(1/2 * -3)}

= 9 ^(1/2)all to the power of -3

= 3 ^-3

= 1/(3 ³)

= 1/ 27

Melody23 Okt 2013

+118689

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"The number was up by 6.5% on the 2010 number."

This means that the 2011 enrolment is greater than the 2010 enrolment.

Somethimes words can be difficult to get your head around.

My answer is not wrong.

Melody23 Okt 2013