inverse e question? (1 Viewer)

[MissGeorgie]

hey,
im kinda stumped on this question:


f(x) = e (to the power x) - 4

find the inverse function and state its domain


any help with this would b great coz i cant find it in my text books anywhere????

thanks

 

[Estel]

let y=e^x-4
Then the inverse is x = e^y-4
ln(x+4) = ylne
y = ln(x+4)
Hence the inverse function is
f-1(x) = ln(x+4)
With domain x > -4

Note: how do u do supscripts and superscripts?

 

[MissGeorgie]

thanks but why does x = e^y - 4????



isnt it lny = x - 4??

 

[Estel]

To get the inverse of something, you simply interchange x and y (I think.... this is from work I did in a Yr 10 option topic).

How did you get lny=x-4?

 

[MissGeorgie]

lol, i dont no......took the log of both sides?

wouldnt hav a clue, i kinda didnt listen 4 this topic....or any other 4 that matter, i'll just take your word for it.

thanx

 

[MissGeorgie]

lol, actually, now that i read it, it does make sense.

thanks heaps

 

[~*HSC 4 life*~]

Estel do you accelerate maths?
how do you allready know inverse trig? i thought it was an HSC 3u topic!

 

[Estel]

I don't accelerate.
I did the Yr 10 Logarithms option topic.

 

[MissGeorgie]

yay..... =S y would u bother?? logs and exponetials r sooooo boring

 

[Estel]

We did it in class... we did 5 option topics:
Circle Geometry, functions and logarithms, polynomials, matrices, surveying.

 

[CrashOveride]

matrices...isnt that like 1st year uni =p

 

[MissGeorgie]

well thats gotta suk!!

 

[CrashOveride]

MissGeorgie what book are you using for 3unit

 

[Estel]

Our teacher made us do matrices as we had quite a bit of time left and she said it might be useful to us later.

 

[hatty]

yeah for inverse functions all u gotta do is change x and y around, then make y the subject

 

[CrashOveride]

Originally posted by hatty
then make y the subject

yeah...in a test a while back..i left x as the subject coz the question said put it in like any form or something and i thought i could get away with it

 

[MissGeorgie]

i use coroneos vol 2 and jones and couchman vol 2. not very exciting really.

iv got 2 and 3u assesments this week =S i should prob start doing sum work....lol...nah....too much effort

 

[hatty]

Originally posted by CrashOveride
yeah...in a test a while back..i left x as the subject coz the question said put it in like any form or something and i thought i could get away with it

well now u learnt ur lesson