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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Bree:
What is the product of 3x^y(3xy^+2x)

Hi Bree
Could you check this question please, that 'hats' ^ are not in the right place(s).

MelodyMar 21, 2014

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Guest:
2000=(-8.255*10^-5)z^2+1.05z+1110

[input]2000=(-8.255*10^-5)z^2+1.05z+1110[/input]

yuck!
It is just a horrible quadratic equation so you can take the 2000 to the other side and use the quadratic formula

0=(-8.255*10^-5)z ²+1.05z+1110-2000
0=(-8.255*10^-5)z ²+1.05z-890

[input]0=(-8.255*10^-5)z^2+1.05z-890[/input]

MelodyMar 21, 2014

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Guest:
what is 2*sin

Nothing
I has to be 2sin(some angle)

MelodyMar 21, 2014

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chris434:
2z+4=-4

Subtract 4 from both sides then think about what to do next.

whatever you do you must do to both sides. !

MelodyMar 21, 2014

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Hanief:
x+109.9/x=6.7 how to get the value of x?

Chris has answered the question that you asked which is

x+ (109.9/x) =6.7

Is that what you intended?

MelodyMar 21, 2014

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BreeziBee:
how do I solve: 81x^2+144x+64=0

(a+b) ²
=(a+b)(a+b)
=a ² + 2ab + b ² You need to memorise this!

(9x) ² = 81x ²
8 ² = 64
2*9x*8 = 144x

So like Chris said, this is a perfect square factorisation

MelodyMar 21, 2014

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Sorry Chris,
I just realised you answer is the same as mine. I had better look at what you did a little more thoroughly.
(I think my way is a little easier to understand)

MelodyMar 21, 2014

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squidhardy:
The initail value of a car is $25,000. After one year, the value of the car is $21,250. Write an exponential function to model the expected value of the car. Estimate the value of the car after 5 years.

Hi Squidhardy and CPhill
there is a formula but I want to show you the logic behind it.
Say the deflation rate is r per year. This will mean the following

Original value = $25000
After 1 yr = $25000 * (1-r)
After 2 yr = $25000 * (1-r) ²
After 3 yr = $25000 * (1-r) ³
After 4 yr = $25000 * (1-r) ⁴
After 5 yr = $25000 * (1-r) ⁵
After n years = $2500 * (1-r) ⁿ

the general formula is F _n=P(1-r) ⁿ
Where F is future value and P is the principal value.

so we have
F _n = $25000 * (1-r) ⁿ
and
$25000 * (1-r) = $21,250 [Value after 1 year is used to find r]
1-r = 21250/25000
1-21250/25000=r

1-21250/25000
So the car is depreciating by 0.15 or 15% per year.
1-0.15=0.85

F _n = $25000 * 0.85 ⁿ
F ₅ = $25000 * 0.85 ⁵

25000*0.85^5

So after 5 years the car will be worth $11092.63

MelodyMar 21, 2014

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That is if it shared equally

MelodyMar 21, 2014

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CountryGirl333:
Find the height of a triangular prism with a base length of 10 yards, a base height of 20 yards, and a volume of 600 cubic yards.

Sorry Sam but it is a prism NOT a pyramid so you have used the wrong formula.

The volume of any prism is the area of the cross section (that stays the same) times by the depth, or height or whatever you want ot call it.

I think it is the height of the triangle that is missing although the question could be interpreted differently. The area of a triangle is (1/2)*base*height = (1/2) * 10 * h = 5h yards squared

so
5h*20=600
and you can finish it.

MelodyMar 21, 2014