Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    Guys as you know l am no maths person at all so l just want to check whether l am on the right lines with this question or way off, l actually have 2 answers and 2 completely different ways of doing this so l'll write this one out first and you can all give me your tuppence worth if you wouldn't mind helping an non maths person out please!

    Let F be a function of t. When log10 F is plotted against t, the graph is a straight line. Furthermore, log10 F=3,5 when t=2 and log10 F=6 when t =5. Find an expression for F in terms of t that does not involve logarithms.

    Solution 1

    diff of logs 6 -3.5
    --------------------- 2.4/3 = 0.83
    diff of logs 5 -2

    Thus the line has the slope 0.83 and passes through the point t2
    Thus the line has the equation log10 F -3.5 = 0.83 (t-2)

    0.83 - 2* 0.83 =0.83 + 3.5-1.66
    = 0.83 +1.84

    then raise the powers 10^0.83 * 10^ 1.84

    F = 69.2 * (6.8)t

    Is this right or not?

    Thanks in advance
    • Political Ambassador
    Offline

    3
    ReputationRep:
    Political Ambassador
    (Original post by Karen72)
    Guys as you know l am no maths person at all so l just want to check whether l am on the right lines with this question or way off, l actually have 2 answers and 2 completely different ways of doing this so l'll write this one out first and you can all give me your tuppence worth if you wouldn't mind helping an non maths person out please!

    Let F be a function of t. When log10 F is plotted against t, the graph is a straight line. Furthermore, log10 F=3,5 when t=2 and log10 F=6 when t =5. Find an expression for F in terms of t that does not involve logarithms.

    Solution 1

    diff of logs 6 -3.5
    --------------------- 2.4/3 = 0.83
    diff of logs 5 -2

    Thus the line has the slope 0.83 and passes through the point t2
    Thus the line has the equation log10 F -3.5 = 0.83 (t-2)

    0.83 - 2* 0.83 =0.83 + 3.5-1.66
    = 0.83 +1.84

    then raise the powers 10^0.83 * 10^ 1.84

    F = 69.2 * (6.8)t

    Is this right or not?

    Thanks in advance
    not sure what "diff of logs" is getting at, but I'd advise you to keep the exact value of the slope, i.e

    \frac{2.5}{3}

    Now, you get

    \log_{10} F - 3.5 = \frac{2.5}{3}(t-2)

    so

    \log_{10} F = \frac{2.5}{3}(t-2) + 3.5

    so

    \displaystyle F=....

    Hint:

    \log_{10} 100 = 2

    because

    10^2 = 100
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Indeterminate)
    not sure what "diff of logs" is getting at, but I'd advise you to keep the exact value of the slope, i.e

    \frac{2.5}{3}

    Now, you get

    \log_{10} F - 3.5 = \frac{2.5}{3}(t-2)

    so

    \log_{10} F = \frac{2.5}{3}(t-2) + 3.5

    so

    \displaystyle F=....

    Hint:

    \log_{10} 100 = 2

    because

    10^2 = 100
    Name:  photo copy.jpg
Views: 65
Size:  90.5 KB

    The above is what we've been taught and l've no idea if the question l've done is the same thing as l said before the maths lecturer was sacked and we're 4 weeks from exams on a subject that is not my area at all, l am actually an Anatomy student l know hee haw about about Maths on any level so l really need some help!

    Thanks for the help btw l really do appreciate it!
    • Political Ambassador
    Offline

    3
    ReputationRep:
    Political Ambassador
    (Original post by Karen72)
    Name:  photo copy.jpg
Views: 65
Size:  90.5 KB

    The above is what we've been taught and l've no idea if the question l've done is the same thing as l said before the maths lecturer was sacked and we're 4 weeks from exams on a subject that is not my area at all, l am actually an Anatomy student l know hee haw about about Maths on any level so l really need some help!

    Thanks for the help btw l really do appreciate it!
    What's shown in the pic is correct, but I 'd say it's a bit lazy as they haven't maintained the exact values.

    Take this example. Here,

    \frac{2.5}{3} = 0.83333.....

    so it wold be better to keep it as a fraction rather than approximate it to 0.83.

    However, if it's acceptable on your course, you may approximate like that.

    Make sense?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Indeterminate)
    What's shown in the pic is correct, but I 'd say it's a bit lazy as they haven't maintained the exact values.

    Take this example. Here,

    \frac{2.5}{3} = 0.83333.....

    so it wold be better to keep it as a fraction rather than approximate it to 0.83.

    However, if it's acceptable on your course, you may approximate like that.

    Make sense?

    Yup that makes sense as l said he was sacked for being an idiot and over complicating stuff so l don't really have any faith in his notes!

    But thank you for your help you've been brilliant!
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
    Useful resources

    Make your revision easier

    Maths

    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here

    Equations

    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.