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#1 Re: Help Me ! » Increasing and decreasing concept » Yesterday 19:04:56

hi iamaditya

Thanks.  Ganesh has also been made an administrator.  Is it a promotion?  I feel it's a huge responsibility.  Let's hope I'm up to the task. 

Bob

#2 Re: Help Me ! » Increasing and decreasing concept » Yesterday 00:36:02

hi Zeeshan 01

In order to help you I need to know what you understand and what is new to you.

Q1. Most people learn first about measuring angles in degrees.  Later they learn about another way to measure angles : radians.  Do you know about radians?

Q2. Do you know how to make the graph for sin(x)?  Did you understand the graph I showed in post 6 ?

Q3.  I also do not know where " pi/4 and 3pi/4. " came from.  These are not the answers to either of the questions you asked in post 1.  Why do you think they have anything to do with those questions?

Bob

#3 Re: Help Me ! » % » 2017-06-22 19:27:05

hi Zeeshan 01

You asked

What percent of 25 is 5?

This is the same as asking "If 5 apples out of 25 are bad, what percent is that?"

This screen shot from the percentage page shows how to do this.  And there is also an interactive calculator which will allow you to experiment with percentage values.  I've added that to the screen shot and put a red border around it.  You can change the 80 to 25, and move the slider until it reads ??% = 5.

idKKJTi.gif

Hope that helps,

Bob

#5 Re: Help Me ! » Functions Problems » 2017-06-21 06:56:02

hi denis_gylaev

Think of a function as being a box into which you can input a number and another number is output.  f and g are two such functions.

If you join the output from g to the input for f we get a composite function.  To find out what single function is the same as the composite function you have to apply first g (which means you have an expression in x and put that through the second box for f.

g(x) = 3x + c so the box takes a number, times it by 3 and then adds c.  If that is the input for the f box the output from f looks like this:

2(3x + c) + 7  The input is (3x + c) and this is times by 2 and 7 added.

So the composite function for (f o g) is 2(3x + c) + 7.  You can simplify this yourself.

You might think at first that g o f will give the same result but it doesn't.  First do f ... 2x + 7 and then make this the input into g ... 3(2x + 7) + c

We want these to be equal so just make an equation by putting them equal to each other.  The x terms cancel out (why?) so you're left with an equation for c.

There is a MIF page on this here: http://www.mathsisfun.com/sets/function … ition.html

Note The x comes after the function letter [eg. f(x) not (x) f ]  so when you want to apply a second function you have to put it before the first. eg g(f(x)) means apply f then g to the result.  This can be confusing but think about log(sin(x)) for example.  o is used to indicate that we are combining functions.

Hope that helps,

Bob

#6 Re: Help Me ! » Functions Problems » 2017-06-21 05:35:30

hi denis_gylaev

Q1)  f o g means apply g and then f to the result:

f o g (x) = 2.(3x + c) + 7

Do a similar thing for g o f and set them equal.

Q2)  This will get the equation of the line AB:

By substituting the known values of x and y you can get equations to find a and b.

Q3)  Just set f and g  equal and solve for x.

Bob

#8 Re: Help Me ! » Graphing Functions » 2017-06-16 19:54:51

There are 4 unknowns so, normally, you would need 4 bits of information.  The 3 crossing points isn't enough so I looked for a point on the graph.  If you put x=4 & y=3 you be able to rearrange to find a.  If you then expand the brackets you will be able to find all the unknowns.

Bob

#9 Re: Maths Is Fun - Suggestions and Comments » What is "moderated by" » 2017-06-16 19:45:45

There are some filters but eventually a determined poster will find a way round.

I think making a report speeds up the process of getting someone to delete something.

Bob

#10 Re: Help Me ! » Polynomial help » 2017-06-16 09:42:42

It's ok.  I wasn't offended.  Just cross with myself for missing that.  There's a phrase for it here in the UK: can't see the wood for the trees.

Bob

#11 Re: Formulas » high school inequalities » 2017-06-16 02:02:14

All I can say is they are fundamental to any mathematical theory so can be taken as "unstated" axioms.  The quoted definition uses "OR", so is already using a logical symbol, and the logical symbols "AND" & "IMPLIES" are also used in the axioms.

Bob

#12 Re: Help Me ! » Polynomial help » 2017-06-16 01:59:24

Hi thickness,

Oh yes!  Silly me. dizzy. Obviously, this reveals I have no presence of mind.  In fact, maybe no mind at all.  And it doesn't even have to be cubic shame

Bob

#13 Re: Help Me ! » Graphing Functions » 2017-06-16 01:47:21

Hi butterscotchlover2

Welcome to the forum.

Hard to tell from the image I am viewing but it looks like the curve crosses the x axis at 0 1 & 2

That would make the function ax(x-1)(x-2)

Also looks like (4,3) is on the curve which will tell you the value of a.

Bob

#14 Re: Formulas » high school inequalities » 2017-06-13 19:51:07

hi chrislav

It stems from the definition:

Definition : a>=b <=> a>b or a=b

This means that for a and b there are two cases.  And for b and c there are two cases.  Putting these together makes 2 x 2 cases.

I suppose this comes from basic logic theory, or from (probability) trees.

Bob

#15 Re: Formulas » high school inequalities » 2017-06-12 21:09:49

hi chrislav

That wasn't quite what I meant.  There are 4 cases:

case 1.  a > b AND b > c
case 2.  a > b AND b = c
case 3.  a = b AND b > c
case 4.  a = b AND b = c

If you are able to prove the required result for each of the above, then you're done.

Bob

#16 Re: Formulas » high school inequalities » 2017-06-11 21:27:29

hi chrislav

Thanks for the quick reply.  Yes, you can use LaTex.  Look here: http://www.mathisfunforum.com/viewtopic.php?id=4397

That thread goes on for a long time but you'll read enough in the first few posts to get started.

Definition : a>=b <=> a>b or a=b

I think that definition is the place to start.  If you consider separate cases, eg a>b AND b=c, you can show the required result for each case.

Hope that helps smile

Bob

#17 Re: Formulas » high school inequalities » 2017-06-11 18:58:26

hi chrislav

Welcome to the forum.

Some people, looking at these, might say 'isn't it obvious?'  So I'm guessing this is a proof from first principles analysis.  Tp start you need to look at the definition of >=

If you post this back I'll see if I can help.

Bob

#18 Re: Maths Is Fun - Suggestions and Comments » What is "moderated by" » 2017-06-11 07:31:32

hi iamaditya

The website was set up by MathsIsFun and he has administrator status.  That means he can control everything to do with the site.  He has appointed moderators to help with that task and moderators can do some things.  eg.  If I find an unsuitable post (inappropriate language, pictures, advertising for example) I can delete it.  I can also ban a user who abuses the forum.  I have been 'assigned' certain sections of the website to 'keep an eye on'.

My biggest job in this regard is to remove inappropriate adverts and the person who has placed them.  Some guys seem to think it's ok to post a load of junk on our site and I have to stop them doing this.  I used to keep a record of every such deletion but it was taking up too much memory space and taking up too much time, so now I just zap them.


Bob

#19 Re: Maths Is Fun - Suggestions and Comments » Encountered some problem in this question.... » 2017-06-10 21:32:19

hi  KayleXYZ

I didn't solve this that way.  I just expanded (x-1)(x+2)(x-2) and looked at the coefficients.

But using your approach the three equations should be

Bob

#20 Re: Help Me ! » Polynomial help » 2017-06-10 21:22:28

hi Randy123

A polynomial has the form:

You only have 4 constraints so you'd have to assume that a5, a6, .... are all zero.

You can then form 4 equations like this:

I got that one by putting x=2

You'll get three more by putting x=0, x=1 and x=3.

Then you need to use simultaneous equation methods to solve for all the 'a's.

If you can get those equations, but cannot solve them, then post again with your 4 equations.

Bob

#21 Re: Introductions » hello i am a new member , but i want to change my username . » 2017-06-09 20:05:18

hi tonyjaa

Sorry, I've been away and am just catching up on forum threads.

iamaditya is correct.  Moderators cannot do this.  I will pm Mathsisfun.

Bob

#22 Re: Introductions » I'm a new member » 2017-06-01 19:06:42

hi Ayananta

Welcome to the forum.

Bob

#23 Re: Help Me ! » Square root » 2017-05-31 21:15:05

Zeeshan 01 wrote:

N is 0.2 and how x is 1 and y is 0.2

You asked for

Sqrt of 0.2 is  ???

So that makes N=0.2

x is a guess.  It can be any number.  If you chose a value close to the correct answer, then you'll get to an accurate answer more quickly.   But any number will work so I chose x = 1.

Then you calculate y using the formula y = N/x= 0.2/1 = 0.2

Then you calculate the mean average of x and y = (1+0.2)/2 = 1.2/2 = 0.6

That becomes the new x. Repeat until x and y are so close to each other that (x+y)/2 gives the same result.  That's the square root.

Bob

#24 Re: Help Me ! » Help with geometric proof » 2017-05-31 19:28:12

hi Mathegocart

You have sufficient facts for congruency.  Have a look at this page:

http://www.mathsisfun.com/geometry/triangles-congruent-finding.html

Bob

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