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#1 Re: Help Me ! » Can somebody please help me understand... » 2012-09-25 06:33:06

bob bundy wrote:

The square bracket means include the endpoint.  It seems I am assuming too much.  If it doesn't say strictly, I concede the argument.



Thank you for everything!!!!!!! bob bundy!!!!!! plus congrats to owner..admins..moderators etc. for this great site! big_smile cheers!

#2 Re: Help Me ! » Can somebody please help me understand... » 2012-09-25 06:13:35

bob bundy wrote:

hi n1corponic

They are the same because

But the book shouldn't be saying less than and equal to because the graph has a turning point when = so dy/dx = 0

So the value of the function isn't getting bigger.


wow! they are the same indeed! big_smile I feel sooooo much better now!

Well, the book says (-infinity, -1/2*ln3] , so I guess it includes -1/2*ln3 probably because the question doesn't ask where the fuction strictly...increases..that must be it! right?

#3 Re: Help Me ! » Can somebody please help me understand... » 2012-09-25 05:56:59

bob bundy wrote:

OK, here we go.

Your differentiation is correct.  For an increasing function you want dy/dx to be > 0

e^x is always positive so you need

log base e  is an increasing function so the inequality holds if you take logs

Graph below.


Your approach seems wonderful!!! and according to me correct.. but why does the book i have give another..but very similar answer?.. it says x<or=-1/2*ln3  Is it the same but i'm missing smth??

#4 Re: Help Me ! » Can somebody please help me understand... » 2012-09-25 05:45:12

bobbym wrote:


Did you look at a graph at all?

Hi bobbym! smile I took a look at the graph in wolframalpha or smth..but it won't help on my future exams.. if i do not know how to find the answer on my own.

#5 Help Me ! » Can somebody please help me understand... » 2012-09-25 05:17:42

Replies: 12 we find the interval where the function e^x-e^(3x) is increasing... the derivative is e^x[1 - 3e^(2x)]. I have the answer but I feel lost.. hmm

#6 Re: Help Me ! » Natural logarithms problem (ln) » 2012-09-10 22:01:21

Hi Bobbym! I don't think i have to find a rational number. Usually the answer to these logarithmic problems is smth like x=ln3/ln5 .To answer your great questions:

1)It comes from the book called Essential Mathematics for Economic Analysis 4th edition on page 123 problem 3.(a)
2)I am mostly interested in the logical thinking process in these kind of problems.

#7 Help Me ! » Natural logarithms problem (ln) » 2012-09-10 21:29:24

Replies: 3

Hello all! I am new here and I am a student having a hard time in math. I have the following natural logarithms  problem and it is giving a hard time. Can someone please help with the solution? And also if possible evaluate the difficulty of this problem?

Solve for x: 4^x-4^(x-1)=3^(x+1)-3^x

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