Melody

921 Questions
34315 Answers

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Mathigon website

I just discovered a site called mathigon

https://mathigon.org/dashboard
read more ..

Melody Apr 2, 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. read more ..

Melody Mar 16, 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 read more ..

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Melody Mar 15, 2022

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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

off-topic

Melody Mar 13, 2022

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WELCOME BACK CPHILL !

Melody Feb 11, 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. read more ..

Melody Feb 1, 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 read more ..

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Melody Jan 9, 2022

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HAPPY BIRTHDAY CHRIS!

Melody Dec 20, 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 read more ..

off-topic

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Melody Nov 4, 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

off-topic

Melody Oct 29, 2021

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A burn on a person’s skin is in the shape of a circle. If the radius of the burn is decreasing at the rate of 0.05 cm per day when it is 1.0 cm, what is the rate of decrease of the area of the burn at that instant?
A for area, t for time in days, r for radius in cm

A=pi*r ²
dA/dr = 2*pi*r

dr/dt = -0.05

dA/dt = (dA/dr) * (dr/dt) = 2*pi*r * -0.05 = -0.1*pi*r

When r=1,
dA/dt = -0.1*pi*1 = -0.1pi = -0.314
The instantaneous decrease in area is approx 0.314 cm ²/day

MelodyOct 22, 2013

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Factors of 39 are numbers go into 39 to give a whole answer.
There are 4 of them and you can find them by yourself.

MelodyOct 22, 2013

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Answer is correct but if x>-3 and x<1 then
x must be between -3 and 1
so
-3<x<1

MelodyOct 22, 2013

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this question really does not lend itself to elimination method but here it is.
This is just one way to go about elimination, there are other ways you could have gone about this.

multilply the first one by 2 and swap sides

2(-5/7-11/7*x)=-y*2
-10/7 - 22x/7 = -2y
-2y = -10/7 - 22x/7
So now the equations are

-2y = -10/7 - 22x/7 and
+2y = 7+5x

now add
-2y+2y = -10/7 + 7 - 22x/7 +5x
0 = -10/7 + 7 - 22x/7 +5x

It is easier now just to multiply everything by 7 and then to solve for x
Once you solve for x substitute it back into one of the original equations to get y.

MelodyOct 22, 2013

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one quarter of the total

MelodyOct 22, 2013

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Assuming that a zero can go anywhere I think it is

10^9

MelodyOct 22, 2013

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With repetition it is 10^5 = 100,000

Without repetition, but where order still matter, it is 10P5 = 30,240

I think that is right anyway.

MelodyOct 22, 2013

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How many digits in a zip code?
is it 0 to 9 that are used.
excuse my ignorance but I am not from USA.

MelodyOct 22, 2013

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3x^2+x-2=0

3x ² + x = 2

3(x ² +(1/3)x) = 2

x ² + (1/3)x = (2/3)

now [(1/3) divided by 2] squared = 1/36: add this to both sides

x ² + (1/3)x + (1/36) = 2/3 + 1/36

(x + 1/6) ² = 25/36

x + 1/6 = +5/6 OR x + 1/6 = -5/6

and you can finish it.

MelodyOct 22, 2013

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MelodyOct 22, 2013