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#1 Re: Exercises » Question » Yesterday 06:13:35

Well it is.  I don't know why you're surprised.  Am I missing something?  If you have that software then give it a try.  If you don't then stop worrying.


#2 Re: Exercises » Question » Yesterday 03:57:37

Not exactly.  Microsoft Excel uses it to mean:

You will find a lot of helpful maths on this site: … ithms.html

When you want a new topic, use the search engine at the top of every page, or the cross-links between pages.


#3 Re: Exercises » Question » Yesterday 01:58:24

to the power of e  some say exp


#4 Re: Exercises » Question » Yesterday 01:09:15

We have met this before.  ln and e^ are inverse functions.

If y = e^x then x = ln(y)

So if you raise ln(something) to the power of e, the ln and e cancel out, and you're left with the 'something'  ... in this case just y

It's like doubling one half of something.  Doubling 'undoes' the effect of halving so you get back to where you started.

One way to define a log is to say it has this property.

eg  If y = a^x then we define the log of y (in base a) to be x.

Or you can say, if I have a number y, what power of 'a' will give me y.  This power of 'a 'is called the log of y.

eg.  What power of 10 will give me 1000 ?  Answer 3.  So we say 3 = log(1000) in base 10.

So you can always re-write a power expression as a log expression or the other way round.


#5 Re: Exercises » Question » 2017-04-28 23:43:00

Is it possible y=e^(alnx)???

You can differentiate this:

Replacing the first part by y brings you back to my earlier answer. 

My version is the one that you will find in lists of standard differentials such as: … etable.pdf


#6 Re: Exercises » Question » 2017-04-28 22:03:36

are different ways of writing the same thing.  ln was the quickest for me.  (But not as it turned out, as I've had to add this post smile )


#8 Re: Exercises » Question » 2017-04-28 19:50:05


If you take logs of both sides (base e) then

Differentiate with respect to x:


#9 Re: Help Me ! » Equation » 2017-04-28 19:42:20

Zeeshan 01

How much importance did slope play...??!!!!

If you want two lines to be parallel on a graph, then slope is everything!

In this diagram AC and BE are parallel lines.  ABD is a vertical line, and both BC and DE are horizontal.


The slope of line AC is AB/CB.

The slope of BE is BD/ED.

The triangles ABC and BDE are similar because AC // BE ; AB // BD ; and BC // DE so all three angles of one triangle are equal to the equivalent angles in the other triangle.  // is an abbreviation for 'is parallel to' .

If the two triangles are similar then their corresponding sides are in the same ratio

So parallel lines have the same slope values.


#10 Re: Help Me ! » Equation » 2017-04-28 05:21:01

Let us try to follow the numbers as an equation is re-arranged.

The slope is -a/b

Any line parallel must have the same slope, -a/b

You could do this:

Example Find a line parallel to 3x + 5y - 7 = 0

The slope is -3/5 so I'll make up a new line with the same slope:

Please notice that the ratio 3:5 appears all the way through this problem.  Once you realise this will always happen, you don't need to make the slope intercept form to answer the question.  It is easy to write answers down just by using 3 and 5. 

Like this.  Here are some more possible answers:

3x + 5y -12 = 0
3x + 5y + 100 = 0
6x + 10y + 20 = 0 [because this is the same as 3x + 5y + 10 = 0]
300x + 500y + 10000 = 0


#11 Re: Help Me ! » Equation » 2017-04-27 23:19:31

hi Zeeshan 01

In that line the 1 in 1x and the 3 in 3y completely determine the slope of the line.  The -9 only affects where the line crosses the axes.

As a parallel line must have the same slope,  any of the following will be parallel:

x + 3y + 10 = 0
x + 3y +100 = 0
x + 3y = 97


2x + 6y + 17 = 0 because the ratio is still 2:6 = 1:3

So these will also work:

2x + 6y + 100 = 0
12x + 36y - 1000 = 0


0.5x + 1.5y + 1.23456 = 0

You just have to make sure that in the equation ax + by + c = 0,      a:b = 1:3

So, there plenty to choose from (an infinite number as there's an infinite number of parallel lines).  Just make sure you don't accidentally pick the same line as the question:

eg.  2x + 6y - 18 = 0 is just the question line doubled.

Please make up one of your own rather than pick one of mine.  That will show you have understood.


#12 Re: Dark Discussions at Cafe Infinity » 2015 UK General Election » 2017-04-27 21:25:15

Yes, I agree.  That's why I put 'excuse' in inverted commas.

There's another reason too.  In three year's time, when she has to have an election, the Brexit deal will be known by all.  She may not be so popular then.

But didn't she argue that the Scottish people shouldn't be allowed a referendum until the facts are known.  That's funny; it's almost as if she makes up the rules to suit herself. 


#13 Re: Help Me ! » Distance » 2017-04-27 21:08:46

Yes.  They are on the same horizontal line.


#14 Re: Help Me ! » Distance between parallel line » 2017-04-27 21:06:59

Yes.  That's the formula I was referring to.

note the bracket:

D=(ax1+by1+c)/sqrt (a^2+b^2)


#15 Re: Dark Discussions at Cafe Infinity » 2015 UK General Election » 2017-04-27 21:04:18

With the combination of global warming and Brexit, I expect we'll be growing our own bananas soon here in the UK.  smile

Theresa May's 'excuse' for calling an early general election: She's fed up with the opposition MPs actually trying to prevent her from doing what she wants.  She's hoping there'll be no opposition at all after June 8th.  She may (no pun intended) get her wish.

Before the referendum she was a Remain supporter.  Her election constituency voted in favour of Remain in the referendum.  Odd that she is now a Brexit supporter.


#16 Re: Dark Discussions at Cafe Infinity » 2015 UK General Election » 2017-04-27 20:00:39

hi Agnishom,

An oft-cited objection to Britain being a member of the European Union is that the EU forces silly 'directives' on member states.  The bent banana directive has been used for years by Eurosceptics as a reason that belonging is foolish.  The Wiki article explains quite well the true facts. … nt_bananas

Just in case you think British citizens can only buy straight bananas here is a photo of the shelves at a well known supermarket not far from my house:


During the 'Brexit' debate a lady (in the audience) said on national television that she had decided to change her vote from 'Remain' to 'Leave' because she wanted to be able to buy bent bananas.  She was widely ridiculed but the Daily Mail continued to run the directive criticism story.

The Leave campaign had a battlebus:


The financial editor of the BBC demonstrated on Tv that this figure was completely untrue.

The (unbiased) head of the UK Statistics Authority, Sir Andrew Dilnot, censured the £350m a week claim and told the Leave campaign they should alter it.  They were also widely criticised in the media.

They changed to 'poster' to read '50 million a day' !


The day after the referendum result Nigel Farage admitted that it was a lie.

Sometimes I despair of there ever being intelligent debate in this country.  sob sob!


#17 Re: Help Me ! » Distance between parallel line » 2017-04-27 19:21:57

If you want to do this using that formula you need (x1,y1) to be (any) point on one line, and (x2,y2) to be a nearest point to it on the other line.  You could proceed like this:

step 1: choose a point on line 1 ; A = (x1,y1)
step 2: calculate the gradient of the line through A perpendicular to line 1.
step 3: calculate the equation of the perpendicular line (say, line P)
step 4: calculate where line 2 crosses line P ; B = (x2,y2)
step 5: calculate the length of AB.

I think it is quicker to calculate the difference between the intercepts = D.  Then the angle of slope of the lines, θ.  Then the required distance is D.cos(θ)

There is also a formula for calculating the distance from a known point to a known line.  Ask again if you want this formula.


#18 Re: Help Me ! » Equation » 2017-04-27 19:10:49

hi Zeeshan 01

The scalar product is defined that way.  It is useful because the cosine of a vector gives the component of that vector in a certain direction.  So the scalar product can be used to determine

eg1.  Magnetic flux is the dot product of the magnetic field and the area vectors.
eg2. Work done by a force is F.d where the Force is F, and d is the vector for the distance moved.


#19 Re: Help Me ! » Distance » 2017-04-26 23:31:16

I have edited my previous diagram.



#20 Re: Help Me ! » Distance between parallel line » 2017-04-26 20:22:21

Your sign is wrong in 2x?

Maybe this was deliberate so that you could work your question on your own rather than just copy a model answer.  Anyway, why does it matter?  You wanted to be shown the method and you have been shown.


#21 Re: Help Me ! » Equation » 2017-04-26 20:16:08

It is the same formula.  tanith has re-arranged it to make the angle the subject to make it easier for you.

Note also: it is called the 'dot' product because a 'dot' is used rather than a times sign.  It's best to stick to this because {vector 1} x {vector 2} means use the 'vector' product which is a very different thing.


#22 Re: Help Me ! » collision » 2017-04-26 20:04:09

First question  What have you got for the change in KE?

next question: Looks like the first with values for the velocities.

he only takes into consideration the i direction which does not make sense to me

for m you have shown that W = 0 so there is no change of KE in the y direction ( zero to zero)

For Km you know C = B so again no change in KE in the y direction.


#23 Re: Help Me ! » Equation » 2017-04-26 19:57:11

hi Zeeshan 01

You can make an equation for this using the 'scalar' or 'dot' product.  Do you what a scalar product is?


#25 Re: Help Me ! » Triangle Law Of Addition » 2017-04-24 20:29:19

Two ways to say the same:

a < b + c is the same as b + c > a

a is shorter than b + c is the same as b + c is greater than a.


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