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# C3/C4 Edexcel - functions, and exponentials

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1. Hey! Right so I've already emailed my teacher, looked around on MyMaths/textbooks etc and so far, no good answers, so I have two questions:

1. How do I find the range of a function?
Simple, I know, but I'm just really struggling with how to do it.

2. What on Earth am I doing with rates of change when t is infinity??

Thanks in advance guys
2. (Original post by sadiowitch)
Hey! Right so I've already emailed my teacher, looked around on MyMaths/textbooks etc and so far, no good answers, so I have two questions:

1. How do I find the range of a function?
Simple, I know, but I'm just really struggling with how to do it.

2. What on Earth am I doing with rates of change when t is infinity??

Thanks in advance guys
1) Use the domain (possible x values) to consider the values of the function ie the 'y' values - a sketch might help.

2) Can you give an example? Usually you have something like e^-t which tends to zero.
3. (Original post by Muttley79)
1) Use the domain (possible x values) to consider the values of the function ie the 'y' values - a sketch might help.

2) Can you give an example? Usually you have something like e^-t which tends to zero.
This is the part I don't understand!

Attachment 529915529917
Attached Images

4. (Original post by sadiowitch)
This is the part I don't understand!

Attachment 529915529917
As I said the term e to the power of -t tends to zero.
5. (Original post by Muttley79)
As I said the term e to the power of -t tends to zero.
Ah sorry, just realised why what I said doesn't make sense! It's because this is the answer for a), I don't understand how you get from this to the equation for m in c)!
6. (Original post by sadiowitch)
Ah sorry, just realised why what I said doesn't make sense! It's because this is the answer for a), I don't understand how you get from this to the equation for m in c)!
As t gets large e^t gets large so we have a big number divided by a big number + 1 (which makes little difference to a big number). So effectively the numerator and denominator are the 'same' ie the fraction is 1.

It's like 1000/1001 then 10 000/10 001 then etc
7. (Original post by Muttley79)
As t gets large e^t gets large so we have a big number divided by a big number + 1 (which makes little difference to a big number). So effectively the numerator and denominator are the 'same' ie the fraction is 1.

It's like 1000/1001 then 10 000/10 001 then etc
Ooooooooh okay, thank you so much
8. (Original post by sadiowitch)
Ooooooooh okay, thank you so much
You are welcome

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