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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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

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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

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0

what does 3 over 5 times 1 over 9 equal

(3*1) / (5*9)

Melody30 oct 2013

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calculate the volume of water a semi-cylindrical trough could hold when full if the dimensions were 4 meters wide and 20 meters long

V = (1/2) * pi*r ²h

Where r=2 and h=20

Melody30 oct 2013

+118696

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need help with adjacent angles and a pair of vertical angles

What help?

Adjacent angles have the same vertex and a common arm (ray)

Vertically opposite angles are the angles opposite each other on an X . They are always equal.

Is that what you wanted to know?

Melody30 oct 2013

+118696

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y=x^2+7x-18
Hopefully you will recognise that this is a parabola because of the xsquared and that is concave up because of the invisible + in front of the xsquared term.
First you try to factorise
You look for two numbers that multiply to -18 and add to 7
since they mult to a negative number, one must be positive and the other negative
since they add to a positive number the bigger one will be the positive one +9 and -2 work.
so
y=(x+9)(x-2)

now to look for some points.
When y=0 either x+9=0 OR x-2=0
When y=0 either x=-9 OR x=2
so 2 points are (-9,0) and (2,0)
Its a parabola so the axis of symmetry is half way between these 2 'roots' that is x=(-9+2)/2 = -3.5
substitute x=-3.5 into the original equation to get the value of y (this will give you the vertex)
It is also easy to find the y intercept. The equation of the y axis is x=0 so substitute x=0 into the original equation and you will get y=-18
now you have 4 points and you know its a parabola so you can graph it.

Melody30 oct 2013

+118696

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Sorry 'cuvica' does not translate so I don't know what you mean.

Melody30 oct 2013

+118696

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what is a geometric series?

http://en.wikipedia.org/wiki/Geometric_progression (this is a web site if you want to take a look)
Now,

3,6,12,24,48

43046721, 14348907, 4782969, 1594323,

27, 3, 1, 1/3, 1/9, 1/27

2,-6,18,-54

are all examples of GPs (geometric progressions)
Geometric Series are geometric progressions with + signs inbetween each term.

GPs have a first term referred to as 'a' or 'a ₁' and a common ratio referred to as r

so the first term is 'a' (same as T ₁)
the second term T ₂ is a*r = ar
the third term T ₃ is the second *r = ar*r = ar ²
the forth term T ₄ is the third *r = ar ²*r = ar ³

the nth term called T _n or (sometimes a _n depending on what country you are studyinging in) and you can substitute in any value for n is
T _n= ar ^(n-1)

I don't know how good your algebra is but in the examples above can you find 'a' and 'r' of each one? There is a formula to do this but if you think hard you might not need the formula.

I hope you find this interesting.

Melody30 oct 2013

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Melody30 oct 2013

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2=1.06^n

log2 = log1.6^n

log2 = n*log1.6

log2/log1.6 = n

then you do it on your calculator and get n is approx = 1.474769847

If you have not studied logs yet this will not make any sense.
I had a quick look on the internet to see if I could find a site that will help.
There a lots of sites for people with a basic understanding but I didn't find an intro site.
Basically though, a log is an exponent (I'd call it a power but exponent seems to be the more international name.)
anyway, I hope this was of some interest to you.

Melody30 oct 2013

+118696

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The volume of a sphere of radius "r" is V=4/3pi r cubed. How do i find r and rationalize the denominator?

V=4/3pi r cubed
V=4pi/3 *r cubed

multiply BOTH sides by 3/(4pi) and you get

3V/(4pi) = r cubed

r = [ 3V/(4pi) ] ^(1/3)

I don't believe that you can rationalize the denominor, pi to the power of something will always be on the bottom and pi is an irrational number.

Melody30 oct 2013

+118696

0

a wave has a frequency of 22hz and a wavelength of 4.0m. what is its velocity

Hertz measures cycles per second
A cycle is a wavelength (in length)
so
22 hertz = 22*4 m/s

Melody30 oct 2013