Melody

921 Questions
34315 Answers

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Mathigon website

I just discovered a site called mathigon

https://mathigon.org/dashboard
lee mas ..

Melody 2 abr 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. lee mas ..

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 lee mas ..

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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

Fuera tema

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. lee mas ..

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 lee mas ..

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Melody 9 ene 2022

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HAPPY BIRTHDAY CHRIS!

Melody 20 dic 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 lee mas ..

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Melody 4 nov 2021

-10

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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

Fuera tema

Melody 29 oct 2021

+118687

0

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

Melody22 oct 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.

Melody22 oct 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

Melody22 oct 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.

Melody22 oct 2013

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one quarter of the total

Melody22 oct 2013

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Assuming that a zero can go anywhere I think it is

10^9

Melody22 oct 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.

Melody22 oct 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.

Melody22 oct 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.

Melody22 oct 2013

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Melody22 oct 2013