Miembros: Melody

Jedithious:
Hello,

I was wondering if anyone knows of any apps that can graph such things as ellipses, circles, and hyperbolas?
I certainly have a few apps in which you can enter a function and get a graph for it, but what about being able
to input such things as the focus, directrix, and endpoints in order to come up with conic sections?

Thanks

hi Jedithious.
The Web2 calc does some graphing
then there are these ones.
https://www.khanacademy.org/partner-content/pixar/pixar-parabolas2/pixar-parabolas-3/e/parabola_intuition_2 (this site was suggested by Stu)
https://www.desmos.com/calculator
http://www.wolframalpha.com/input/?i=3%5E%2856%29

the khanacademy one might be of particular interest for parabolas.
Desmos is great for general graphing and you can add in sliders and hence change the value of focal length etc.

I don't know that any will be exactly what you want. If you come up with a great site on your own let us know about it please.
You have a couple to check out anyway.

Melody7 abr 2014

+118730

Chad:
In triangle ZXY, m<Z=111 degrees, y=6 ft, z=29.7 ft Find m<Y

You need to use the sine rule

z/sinZ = y/sinY

Is that enough help.
Try it and get back to me if you have problems.
Please show me what you have done so I know what the problem is.

Melody7 abr 2014

+118730

Boykells:
Which function increases by 1/3 every time the x- increases by 1?
A) y=3^x
B) y=3x+1
C) y=(1/3)^x
D) y=1/3x+1

This would mean that the slope (gradient) was always the same, which means that it must be a straight line.

The gradient is rise/run = 1/3 divided by 1
So what is 1/3 divided by 1?

The formula for a line is y=mx+b
b is the y intercept and it has nothing to do with the slope.
m is the gradient.

This should be enough hints. See if you can work it out.

Melody7 abr 2014

+118730

You are right Anonymous4338,
Reinout has shown me that it 2 2s make a really awesome fish.

Melody7 abr 2014

+118730

mathcalc:
A girl wants to knit a scarf 1 2/5 meters long. On Monday, she knits 1/4 of the scarf. On Tuesday, she knits another 45 cm. What fraction of the scarf has she knit in total?
Please no algebra

Hi mathcalc

We definitely do not need algebra for this one

2/5 = 4/10 = 0.4 so 1 2/5 metres is 1.4metre = 140cm

1/4 of the scarf is 140cm divided by 4 = 35cm

She has knitted a total of 35+45 = 80cm

The fraction she has knitted is the amount she has knitted divided by the total length that the scarf will be. 80/140 = 8/14 = 4/7

Melody6 abr 2014

+118730

51026:
how do you solve 1 step inequalitys

Try working through this page.
http://www.mathsisfun.com/algebra/inequality-solving.html

Highlight the address -> left click -> choose 'goto'.

Melody6 abr 2014

+118730

mrlm1105:
If the hot water tap can fill a bathtub in 60 minutes, and the cold water tap fills it in 30 minutes, how many minutes does it take when they are running together?

First you should think about what would be a reasonable answer. If both taps are running then it is going to take less time than if only one was running. So the answer will have to be less than 30 minutes. Always do reasonableness checks.

You can do this with algebra if you want but i'm going to do it an easier way.
you will get the same answer no matter how much water the bath holds so I am just going to say that it is a 60L bath. That will be an easy number to work with.
The hot water would fill the 60L in 60 minutes. That's 60/60 = 1 L per minutes
The cold water would fill the 60L in 30 minutes. That's 60/30 = 2 L per minutes
Together that will run (1+2) = 3L/ 1min
this can be said the other way around It will take 1 minute to run 3L = 1min / 3L
You have 60L to run
1min/3L * 60L = 20minutes (If you write your fractions upright you will see that the Litres cancel out!)
That passes the reasonable check. Good!

If you want to do it more generally you can replace my 60L with x L. The answer will be the same.

Melody6 abr 2014

+118730

Hi Reinout,
I've been meaning write a post on LaTex for a while now.
I think there are a lot of different versions.
But this is where i learned most of it. The basics anyway.
I've only been using it for about 4-5 months. I hadn't heard of it before then.
https://www.youtube.com/watch?v=SoDv0qhyysQ&list=PL1D4EAB31D3EBC449
This is the first in a serious of clips done by Michelle Krummel. I think she has done a good job.

I dont think that Alan know LaTex. He uses MathType. (I think)
LaTex is the one that internet users use.
MathType is an add-on in 'ms word'. It is more used for documents.
When I was teaching we did all our type setting using MathType. (or just equation editor which was the free included version with ms office.)
I guess I swapped to LaTex because it is conveniently included in most forums.

Anyway that should get you started.

Melody4 abr 2014

+118730

Hi Stu,
(a)
the graph y=e ^x has a very special property. The y value is equal to the gradient of the tangent.
so
dy/dx also equals e ^x
Reiterating:
If y=e ^x then y'=e ^x

This is your question
f(x)=1-e ^x
You are asked to find the gradient of the tangent to the curve at the point where it crosses the x axis.
In this case y has been replaced with f(x). [Call it f(x) but treat it the same as if it was y]
Any curve crosses the x axis when y=0 or in this case, f(x)=0 This is the x intercept.
Find the x intercept
0=1-e ^x
e ^x=1
x=0
now
f(x)=1-e ^x
f'(x)=0-e ^x = -e ^x
when x=0
f'(0)=-e ⁰ = -1

this is the end of part a. I haven't done b or c yet.
Part b is missing the point - do you know what it is supposed to be?

Melody4 abr 2014

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