Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#2 Re: Help Me ! » Mandy Jane's Corner » Today 03:59:47

Chris,

Great that you want to help smile but, for bar charts you might save yourself some time by using ones from here:

http://www.mathsisfun.com/data/bar-graphs.html

Bob

#3 Re: Help Me ! » Mandy Jane's Corner » Today 03:53:21

hi Chris2 and Mandy Jane,

#6 Re: Help Me ! » Help with proof » Yesterday 20:10:27

hi SPARKS_CHAN,

Mark the centre of the circle as point O.

The angle at the centre of any circle is twice the angle at the edge, made by the same chord.

Bob

#7 Re: Help Me ! » function point » 2015-01-27 22:59:43

hi point,

Welcome to the forum.  smile

I am always a bit wary when someone posts a link like this.  You never quite know where it may lead.  Thankfully yours is genuine.  smile

But you could post your work directly using LaTex http://www.mathisfunforum.com/viewtopic.php?id=4397

This will make it easier for people to follow, and, by copying out sections, they can add, and comment more easily.

Bob

#8 Re: Help Me ! » Simplifying » 2015-01-26 06:06:27

hi demha

Q1. {3[SQRT(3)] + 7}[SQRT(3) - 5]

If this was (a+b).(c+d) you'd have to multiply each term from the first bracket with each from the second:

= ac + ad + bc + bd.

If you do this with the question you'll get a term with root 3 x root 3 = 3, and other terms.  It should simplify to something of the form (p + q.root 3)

Q4.  This is just a substitute and evaluate.

Q5 Yes, do what you say.  To solve for 'r' you need to 'un-do' the formula ... divide by 4/3, and by pi, and then find the cube root of that.


Hope that helps, smile

Bob

#12 Re: Help Me ! » The chain rule » 2015-01-24 12:00:23

That's why I suggested a simple example first.  When I find a bit of maths hard, I look for simple cases first so I can slide into the hard stuff in small steps.

Try it with simple functions and just two points, letting the second move gradually closer to the first.  If you set up the formulas on a spreadsheet it will be easy to change 1.1 into 1.01 into 1.001 ...........

Then change the fixed pint t=1 into t=2 and repeat.  Or change the formulas into harder ones.

Think I'd better sign off now and wash away the literal garden mud and metaphorical middle lane hogging driver anguish.  Good night.  See you tomorrow.  sleep

Bob

#13 Re: Help Me ! » The chain rule » 2015-01-24 11:48:17

With my simple functions

x = 2t so t = (x/2)

Therefore y = (x/2)^2

It would be somewhat harder with the functions you chose.  smile

Bob

#14 Re: Help Me ! » The chain rule » 2015-01-24 11:45:15

Just read your last post.  What I had in mind was something like:

x = 2t
y = t^2

Take t = 1 for one point and t = 1.1 for a second.

Compute delta t, delta x and delta y.

Then change t = 1.1 into t = 1.01 so you're letting delta t tend to zero.

It's easy enough to eliminate the t from the above so you have y as a function of x.  That way you can calculate lim (delta y / delta x) and compare results.

Bob

#15 Re: Help Me ! » The chain rule » 2015-01-24 11:41:14

but I wouldn't want you to stay up on my account!

I've just driven 70 miles round the M25 so my brain is wide awake, even though I'm theoretically tired having spent the day doing jobs for my Mum.  So this is probably a good way to unwind.  smile

Bob

#16 Re: Help Me ! » The chain rule » 2015-01-24 11:38:40

Oh drat, you're not.

Never mind I'm warmed up to it now so I'll carry on.

delta x etc is used for a small but not yet zero amount in the x direction.

So you can start with delta y over delta x, and divide top and bottom by delta t to get

If you let delta t tend to zero then you'd be dividing by zero so you need the small but not yet zero amounts.

Then, is it valid to let the amounts all tend to zero so you get

The rigorous proof of that step is the one that is left out.  You could probably convince yourself it is OK by making up an example, but I suggest easier formulas for x and y in terms of t.

Bob

#17 Re: Help Me ! » The chain rule » 2015-01-24 11:29:56

Firstly, the functions of t.

Choose a value of t and work out x and y, using your formulas.  Plot the point (x,y)

Now choose another value of t and repeat.

You'll get a series of points on the graph.  Those points display that x is a function of y and vice versa. 

I'll post this and see if you're still with me.

Bob

#18 Re: Help Me ! » The chain rule » 2015-01-24 11:27:01

hi Au101,

Yes, i'll explain.  It's a bit past my bedtime, but I'll do it now if you stay online.

Bob

#19 Re: Help Me ! » Help me out everybody » 2015-01-22 21:00:11

hi MaaMood93

Welcome to the forum.

You could:

(1) Become a forum member.

(2) Look at the teaching pages on http://www.mathsisfun.com/   There's enough there to keep you busy for a while.  smile

(3)  Post in the Help Me section of you want more help with something.

Bob

ps.  To graduate to genius level you might consider a brain transplant.  smile

#20 Re: Help Me ! » Moment of Inertia » 2015-01-22 20:45:37

hi Agnishom,

Firstly, consider a thin disc of the cone and work out its M of I.

Then sum up all such moments along the axis of the cone, integrating wrt distance from base to vertex.

Bob

#22 Re: Help Me ! » DIFFICULT (for me) GEO PROBLEMS » 2015-01-22 06:43:58

Well done!  That's my answer to.  smile

Bob

#23 Re: Help Me ! » Looking for confirmation of a proof » 2015-01-21 04:37:56

hi Au101,

I thought it was true because these seem like the rules for multiplying powers.

Anyway, thanks for two proofs.  They both look good to me!  Well done!

Bob

#24 Re: Help Me ! » DIFFICULT (for me) GEO PROBLEMS » 2015-01-20 20:23:36

hi SPARKS_CHAN

These can all be done using this property of circles http://www.mathisfunforum.com/viewtopic.php?id=17799 post 6

You will also need isosceles triangles and angles along a straight line = 180.

Q1. Mark the centre of the circle as point C.  Join K, M, Q, and R to C with radius lines.

Then, for example, MCK = 130, and MRK = 65.

Keep working around the diagram using all the above rules to work out every angle.

Q2.  Similarly, call the centre of the small circle point C.  Join AC and BC.  Once again use the angle properties of a circle.

Q3. Same again.  I used the property to work out AOE and COF, and gradually progressed round the diagram working out every angle.

Hope that's enough of a hint.  Post back if you need more.   smile

Bob

#25 Re: Help Me ! » Looking for confirmation of a proof » 2015-01-20 20:07:12

hi Au101,

That all looks good to me except I would like a bit more to explain this line:

Bob

Board footer

Powered by FluxBB