Crazy confused about this question!

[jlai928]

Hey guys I was doing a past paper (Thursday 7th may 2009 Paper 1) and a question came up that just made sit there for 10 minutes like this -> even AFTER looking at the mark scheme..

For those of you who have it, it's question 6b. I'll type out the full question for those of you who don't. I have no problems with 6a but b just left me blank

(maximum mark: 7)

Let f(x)=e^(x+3)

a) i) Show that f inverse of x = lnx-3.

ii) Write down the domain of f inverse.

b) Solve the equation f inverse = ln(1/x)

The problem is: How do you solve if it isn't equal to anything????? I'm just stuck because all it tells you to do is solve but I'm confused since what do we solve for????

Help would be amazing guys thanks so much. P.s. no copyright/rule breaking intended for releasing a past paper question.

[Rahul]

Solve for x

So lnx - 3 = ln(1/x)

e^(lnx - 3)=1/x

e^(lnx)/e^3=1/x

x/e^3=1/x

x^2=e^3

x=e^(3/2)

[iamyourmum]

wrote out the solution

http://i.imgur.com/2eixdEr.jpg

hope it makes sense

[jlai928]

Solve for x

So lnx - 3 = ln(1/x)

e^(lnx - 3)=1/x

e^(lnx)/e^3=1/x

x/e^3=1/x

x^2=e^3

x=e^(3/2)

Ah didn't see that I was meant to equate lnx-3 to ln(1/x) Thank you so much!

wrote out the solution

http://i.imgur.com/2eixdEr.jpg

hope it makes sense

Couldn't have asked for a more thorough work-through thank you!