The Student Room Group

C3 range and domain

http://pmt.physicsandmathstutor.com/download/Maths/A-level/C3/Papers-Edexcel/January%202007%20QP%20-%20C3%20Edexcel.pdf

oh boy do i love these :colonhash::colonhash::colonhash::colonhash::colonhash:

So for 6a is the domain of f1is xRf^{-1} is\ x\in \mathbb{R} x<2??
Original post by will'o'wisp
...


the domain f1f^{-1} is the same as the range of ff
Reply 2
Original post by the bear
the domain f1f^{-1} is the same as the range of ff


so did i work it out right or is it the same as the domain because you can't have -ve logs
Reply 3
Original post by the bear
the domain f1f^{-1} is the same as the range of ff


but the best bit is when the mark scheme doesn't even give u an answer
http://pmt.physicsandmathstutor.com/download/Maths/A-level/C3/Papers-Edexcel/January%202007%20MS%20-%20C3%20Edexcel.pdf
Original post by will'o'wisp
so did i work it out right or is it the same as the domain because you can't have -ve logs


the domain of f is given as x<2, x e R, which means that ( 4 - 2x ) will always be greater than 0, thus the ln of (4 - 2x ) will go from - infinity to infinity ... this will be the range of f and also the domain of f-1
Reply 5
Original post by the bear
the domain of f is given as x<2, x e R, which means that ( 4 - 2x ) will always be greater than 0, thus the ln of (4 - 2x ) will go from - infinity to infinity ... this will be the range of f and also the domain of f-1


but how does it work?

if i put a number slightly less than 2 in i'll get ln(????)=almost 0

the further i go down the number scale ln(????????) gets bigger

so how can i get a -infinity out of this? there is no real number i can think of which will allow me to get -infinity out of ln(4-2x)

tsrln.png
Original post by will'o'wisp
but how does it work?

if i put a number slightly less than 2 in i'll get ln(????)=almost 0

the further i go down the number scale ln(????????) gets bigger

so how can i get a -infinity out of this? there is no real number i can think of which will allow me to get -infinity out of ln(4-2x)


^^^
Reply 8
Original post by the bear
^^^


so i'm saying xR f(x)>0x \in \mathbb{R}\ f(x)>0???
(edited 7 years ago)
grrr ******** latex

the domain of the inverse of f is just x is all Real Numbers.
(edited 7 years ago)
Reply 10
The domain is R \mathbb{R} since the range of f is R \mathbb{R} .
Original post by the bear
grrr ******** latex

the domain of the inverse of f is just x is all Real Numbers.

????? but i don't get it ;_________;
Original post by B_9710
The domain is R \mathbb{R} since the range of f is R \mathbb{R} .


ok but you can't have an ln(- anything) in here it doesn't work
Reply 12
Original post by will'o'wisp
so i'm saying xR f(x)>0x \in \mathbb{R}\ f(x)>0???


Perhaps it would help if you make a sketch of the graph pf y=ln(42x) y=\ln (4-2x) .
the domain of the inverse is the x values which work with the inverse... they do not have to work with the original function.
Original post by B_9710
Perhaps it would help if you make a sketch of the graph pf y=ln(42x) y=\ln (4-2x) .

hmmm so for any log/ln graph the range will always be [latex x\in \mathbb{R}?

I've just drawn the graph now bc it asks me to in part c
Original post by the bear
the domain of the inverse is the x values which work with the inverse... they do not have to work with the original function.


ok?

Quick Reply

Latest