Charlie Posted September 21, 2005 Share Posted September 21, 2005 I've been trying hours to do 2 questions for my maths homework. I've got the answer but don't have a clue how to get there. Could someone point me in the right direction please? 1) The sketch below shows the graph y=log10 (x+c). Find the value of c. 2) The sketch below shows the graph y=alog2 (x+b). Find a and b I've worked out b to be 4 (which is right), I just can't get a. Answers: 1) 3 2) a= 3 1/3 b= 4 ------ Thanks a lot in advance. Link to comment Share on other sites More sharing options...
Space Posted September 21, 2005 Share Posted September 21, 2005 Mr_Odwin will have a field day with this. Link to comment Share on other sites More sharing options...
bob Posted September 21, 2005 Share Posted September 21, 2005 If you have 'b', then you can work out 'a' just by using two values of 'x' and 'y' from the graph. Link to comment Share on other sites More sharing options...
Charlie Posted September 21, 2005 Author Share Posted September 21, 2005 If you have 'b', then you can work out 'a' just by using two values of 'x' and 'y' from the graph. I've got it down to 10=alog2(8). What do you do with the 8 in the brackets? Can you just take it away to get 2= alog2? Then a=log2/2? Link to comment Share on other sites More sharing options...
bob Posted September 21, 2005 Share Posted September 21, 2005 Is that a log to the base 2? Link to comment Share on other sites More sharing options...
Dieter Posted September 21, 2005 Share Posted September 21, 2005 Sorry man, it's been a bit long since I've had logarithmic functions, I need a freshen-up Oh snap, that's the next thing we revise >.< Link to comment Share on other sites More sharing options...
Charlie Posted September 21, 2005 Author Share Posted September 21, 2005 Is that a log to the base 2? Yeah (You could just do all the working if you want, but I think it would probably be better for me if you just give me pointers...) Link to comment Share on other sites More sharing options...
Twozzok Posted September 21, 2005 Share Posted September 21, 2005 i'm guessing this is the scottish equivalent to A Level work? we do nothing like this at GCSE... though i'm gonna be doing it at A Level ^_^ Link to comment Share on other sites More sharing options...
Charlie Posted September 21, 2005 Author Share Posted September 21, 2005 i'm guessing this is the scottish equivalent to A Level work? we do nothing like this at GCSE... though i'm gonna be doing it at A Level ^_^ GCSE = Standard Grade (what I did last year) So if A level is the one after GCSE then that is what it is. Highers, they're called. And they're bloody hard. Link to comment Share on other sites More sharing options...
bob Posted September 21, 2005 Share Posted September 21, 2005 Bugger knows.....we only did log to the base e. Wait for Odwin methinks. Althoughhe did say he hated pure maths. There was a dude in the Uni thread who said he was doing maths at Uni. Forget his name though. 1 Link to comment Share on other sites More sharing options...
Charlie Posted September 21, 2005 Author Share Posted September 21, 2005 Bugger knows.....we only did log to the base e. Wait for Odwin methinks. Althoughhe did say he hated pure maths. There was a dude in the Uni thread who said he was doing maths at Uni. Forget his name though. I hope he drops by in the next 30 mins. This is meant to be in for tomorrow.... Link to comment Share on other sites More sharing options...
bob Posted September 21, 2005 Share Posted September 21, 2005 Dude, if you can't do it, then just tell he teacher you can't do it. They can't berate you for something you can't do. Especially if you've tried for two hours. Link to comment Share on other sites More sharing options...
Charlie Posted September 21, 2005 Author Share Posted September 21, 2005 Dude, if you can't do it, then just tell he teacher you can't do it. They can't berate you for something you can't do. Especially if you've tried for two hours. Yeah, I wil. At least I've actually tried the question. She just said "there better not be any blanks". Link to comment Share on other sites More sharing options...
bob Posted September 21, 2005 Share Posted September 21, 2005 She sounds like a witch. Link to comment Share on other sites More sharing options...
Blackfox Posted September 21, 2005 Share Posted September 21, 2005 Logs are awful. I skipped them and still passed my exams.. Link to comment Share on other sites More sharing options...
entropy Posted September 21, 2005 Share Posted September 21, 2005 I think the log10 means it is base 10 so we have: y = log10 (x+c) 0 = log10 (c -2) [from graph] 10^0 = c-2 1 = c-2 [anything to power of 0 is 1] 1+2 = c therefore c = 3 log2 is log to base 2, so solve simultaneously: 1) 10 = alog2 (4+b) 2) 0 = alog2 (b-3) we'll work with 2) first: 0/a = log2 (b-3) 0 = log2 (b-3) 2^0 = b-3 1 = b-3 1+3 = b therefore b = 4 plug b = 4 into 1): 10 = alog2 (4+4) 10 = alog2 (8) 10 = log2 (8^a) [one of the rules, look in your txt bk] 2^10 = 8^a 1024 = 8^a ln1024/ln8 = 10/3 = 3 1/3 3 Link to comment Share on other sites More sharing options...
bob Posted September 21, 2005 Share Posted September 21, 2005 Well entropy owned this thread. Link to comment Share on other sites More sharing options...
The3rdChildren Posted September 21, 2005 Share Posted September 21, 2005 MAAAAATHS. My nemesis. Link to comment Share on other sites More sharing options...
zatoichi Posted September 21, 2005 Share Posted September 21, 2005 Why don't they teach relevant stuff in maths any more? I mean, when are ya gonna use a graph like that? Certainly not buying oranges. Ooooohhh no. You just need good old fashioned arithmetic for that! Link to comment Share on other sites More sharing options...
SupaFry Posted September 22, 2005 Share Posted September 22, 2005 I was once good at maths but now it just hurts my brain. Link to comment Share on other sites More sharing options...
RATM_4_EVA Posted September 22, 2005 Share Posted September 22, 2005 oh god i hate math. Link to comment Share on other sites More sharing options...
Lammie Posted September 22, 2005 Share Posted September 22, 2005 Man I feel really unintelligent. Link to comment Share on other sites More sharing options...
Ramar Posted September 22, 2005 Share Posted September 22, 2005 Logs..mein eyes!! Thank god I dropped Maths after AS. Link to comment Share on other sites More sharing options...
Daniel Posted September 22, 2005 Share Posted September 22, 2005 pfff i start maths at uni next week and ive never used logs to the base 2 only to base ten and e Edit: come to think of it i only did log graphs in physics.. Link to comment Share on other sites More sharing options...
Charlie Posted September 22, 2005 Author Share Posted September 22, 2005 I think the log10 means it is base 10 so we have:y = log10 (x+c) 0 = log10 (c -2) [from graph] 10^0 = c-2 1 = c-2 [anything to power of 0 is 1] 1+2 = c therefore c = 3 log2 is log to base 2, so solve simultaneously: 1) 10 = alog2 (4+b) 2) 0 = alog2 (b-3) we'll work with 2) first: 0/a = log2 (b-3) 0 = log2 (b-3) 2^0 = b-3 1 = b-3 1+3 = b therefore b = 4 plug b = 4 into 1): 10 = alog2 (4+4) 10 = alog2 (8) 10 = log2 (8^a) [one of the rules, look in your txt bk] 2^10 = 8^a 1024 = 8^a ln1024/ln8 = 10/3 = 3 1/3 Thanks. My teacher showed me how to do it today and her way was the same. Link to comment Share on other sites More sharing options...
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