Graphing Logarthim Functions

[ojchase]

I have a packet I'm supposed to have done by Wednesday when school starts and there are some questions about logarithms that are losing me. We did cover them last year but I never really got them. And I need to know how to find the ranges of equations such as y=ln(cos(x)) and y=ln(9-x²). It would seem to me that any number would work in the domain except for one that makes it negative. So that would mean (second one for example) that x would need to be less than the absolute value of 3. So wouldn't the range be from where y is highest (at x=0) to the lowest....but what's the lowest? When x=2.999999, y=-12.023...., but my calculator's graph only goes down to about -1. So I'm totally lost and missing something. Please help

 

[Deleted member 4993]

I have a packet I'm supposed to have done by Wednesday when school starts and there are some questions about logarithms that are losing me. We did cover them last year but I never really got them. And I need to know how to find the ranges of equations such as y=ln(cos(x)) and y=ln(9-x²). It would seem to me that any number would work in the domain except for one that makes it negative. So that would mean (second one for example) that x would need to be less than the absolute value of 3. So wouldn't the range be from where y is highest (at x=0) to the lowest....but what's the lowest? When x=2.999999, y=-12.023...., but my calculator's graph only goes down to about -1. So I'm totally lost and missing something. Please help

ln(fraction) < 0

ln(0) ~ -infinity

 

[ojchase]

ln(fraction) < 0

ln(0) ~ -infinity[/quote]

Seems that way to me too. So why does the graph abruptly stop at the points: (+-2.8571428571,-0.1782482313)?

 

[Deleted member 4993]

I think your calculator does not have enough resolution (within the window you have chosen) to distinguish between 3 and 2.857 on the x-scale.

 

[ojchase]

I think your calculator does not have enough resolution (within the window you have chosen) to distinguish between 3 and 2.857 on the x-scale.

I had kept thinking about this and was using a computer grapher to zoom in easier and I found (and then on my calculator) that this was the case - at almost the exact time the message you'd replied came through. I expected the calculator to give a straight line down or something but not act like it stopped. It didn't even give you the numbers as you traced off the graph. It was like it simply really stopped there. Once I zoomed in far enough it kept going - so now I feel really stupid but oh well.