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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can anyone solve this?
ln(x)-2ln(x^2+1)+1/2ln(3-x^2)

Yes, you can

use
log(x) ⁿ = nlog(x)
log(a) + log(b) = log(a*b)
and
log(a) - log(b) = log(a/b)

MelodyNov 27, 2013

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sec(x)csc(x)-4csc^2(x)

What am i meant to be proving? there is not equal sign.

MelodyNov 27, 2013

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a*b=15
b*c=35
a*c=21
a=?
b=?
c=?

first get b in terms of a
now put the new value of b into the second equation and rearraange to get c in terms of a
put new value of c into third equation and solve for a
that should be enough to get you started.

MelodyNov 27, 2013

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0

y-3/x=0

Okay what you meant was
(y-3) / x = 0
The first thing that you need to recognise is that x cannot be equal to zero because you cannot divide by 0
then
multiply both sides by x and you get
y-3 = 0
so
y = 3 (where x is not equal to 0)

If you graphed this it would be a horizonal line through y=3 but there would be an open circle on (0,3) to show tht this point is not included.

MelodyNov 27, 2013

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y-3/x=0

I am assuming that you mean

y-(3/x)=0

Just add 3/x to both sides

y - 3/x + 3/x = 0 + 3/x

y = 3/x

Is that what you wanted?

MelodyNov 27, 2013

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find x and y
x-y=3
x^2+y^2=29

If x-y=3 then x=3+y
so
(3+y)^2+y^2=29

now expand the brackets, simplify, bring 29 over to the LHS and then sove as a quadratic.
why don't you have a go a this now.
if you get stuck I'll help some more.

MelodyNov 26, 2013

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Moving in relation to what?
If it is moving at 20km/hour and the car next to it is also moving at 20km/hour in exactly the same direction then both cars are stationary in relation to each other.

how about that!

MelodyNov 26, 2013

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Thank you. I love mathematics and I want to share my enthusiasm with others.
If I help others to understand and to enjoy the experience that is all I want.
It is always really nice when you are appreciated even it you are doing what you want to do most.
so again, thank you.

MelodyNov 26, 2013

+118725

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Water from a stream is used to drive a water wheel. The stream provides 6000kg of water per minute to the wheel. The water falls a vertical height of 5 meters.
Show that the maximum power available to the wheel from the water is 5000W. Halp?

okay, I admit it, I don't know about this stuff but
I just googled "what is a watt" and I was told that

1W = 1Kg*m^2 / s^3

So I am just going to use the units and there is a reasonable chance that I will get the right answer.

You have 6000kg/min = 6000/60 Kg/sec = 100Kg/sec
You have gravity which is 9.8m/s^2
You have 5m

Kg/sec * m/s^2 * m = Kg*m^2/sec^3 Well that is the units that I want
100 * 9.8 * 5 = 4900W
If I had rounded gravity off to 10m/s^2 I would have 5000W
This is the maximum because some of the energy will be lost. (eg noise I think but again I don't really know what I am tallking about)

The motto of this story is:

Always use the units to help you

MelodyNov 26, 2013

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1x2x3x4x5x6x7x8x9x10x11x12x13x14x15x16x17x18x19x20

this question is driving me crazy

19*18 ends it a 2 (9*8=72) I'll come back to 20
so 19*18*17 ends with a 4 (2*7=14)
so 19*18*17*16 ends with a (4*6=24) 4
so 19*18*17*16*14 ends with a (4*4=16) 6 I'll come back to 15
so 19*18*17*16*14*13 ends with a (6*3=18) 8
so 19*18*17*16*14*13*12 ends with a(8*2=16) 6
so 19*18*17*16*14*13*12*11 ends with a (6*1=6) 6
9*8=72
so 19*18*17*16*14*13*12*11*72 ends with (6*2=12) 2 I'll come back to 10
7*6=42
so 19*18*17*16*14*13*12*11*9*8*42 ends with(2*2=4) 4 I'll come back to 5
4*3*2*1 = 24
so 19*18*17*16*14*13*12*11*9*8*24 ends with (4*4=16) 6
Now we haven’t done
5*15*10*20 = 5*20*10*15=15000
So we have at least 3 zeros
5*6=30 so there is the 4th zero.

This is really clutsy - there must be a better way of doing it.

By the way, there is only one 'e' in zeros.

MelodyNov 26, 2013