C1 indices

Maths and statistics discussion, revision, exam and homework help.

This thread is sponsored by:
Announcements Posted on
Important: please read these guidelines before posting about exams on The Student Room 28-04-2013
Search Thread
Advanced Search
Sign in to Reply
  1. jessica_anne_clu's Avatar
    1 15-03-2012  18:55
    • Respected Member
    • Location: Leicester
    • Posts: 161
    C1 indices
    How would you find x?...

    4^x=1/4

    thanks
  2. roar558's Avatar
    2 15-03-2012  18:57
    • Overlord in Training
    • Posts: 2,609
    Re: C1 indices
    (Original post by jessica_anne_clu)
    How would you find x?...

    4^x=1/4

    thanks
    ln both sides if you want to show it mathmatically.
  3. raheem94's Avatar
    3 15-03-2012  18:59
    • TSR Demigod
    • Posts: 5,512
    Re: C1 indices
    (Original post by jessica_anne_clu)
    How would you find x?...

    4^x=1/4

    thanks
    e.g.

    2^{2x} = \frac12 2^{2x} = 2^{-1} 2x = -1 x = -\dfrac12
  4. kingtaco's Avatar
    4 15-03-2012  18:59
    • Full Member
    • Posts: 119
    Re: C1 indices
    (Original post by jessica_anne_clu)
    How would you find x?...

    4^x=1/4

    thanks
    What power would you use to get the reciprocal of a number?
  5. jessica_anne_clu's Avatar
    5 15-03-2012  18:59
    • Respected Member
    • Location: Leicester
    • Posts: 161
    Re: C1 indices
    (Original post by roar558)
    ln both sides if you want to show it mathmatically.
    but how would you go about it? I know the answer is -1 but I don't know how you'd get it
  6. james.h's Avatar
    6 15-03-2012  18:59
    • Exalted and Worshipped Member
    • Posts: 1,065
    Re: C1 indices
    In this case, try multiplying both sides by 4:

    4^{x+1}=1

    Can you see the answer now?


    A general approach for any question like this involves logarithms, but I don't think they're covered in C1...?
  7. steve2005's Avatar
    7 15-03-2012  19:00
    • TSR Demigod
    • Location: LONDON
    Re: C1 indices
    (Original post by jessica_anne_clu)
    but how would you go about it? I know the answer is -1 but I don't know how you'd get it
    Just write down the answer. No working required.
  8. raheem94's Avatar
    8 15-03-2012  19:00
    • TSR Demigod
    • Posts: 5,512
    Re: C1 indices
    (Original post by roar558)
    ln both sides if you want to show it mathmatically.
    ln is in C3, while OP is studying C1 so she probably doesn't knows logarithms.
  9. tnetennba's Avatar
    9 15-03-2012  19:00
    • Full Member
    • Posts: 148
    Re: C1 indices
    You could use logarithms:
    Log 4^x = Log 0.25
    x Log 4 = Log 0.25
    x= (Log 0.25)/(Log 4)
    x=-1
    Post rating:
    1
  10. raheem94's Avatar
    10 15-03-2012  19:02
    • TSR Demigod
    • Posts: 5,512
    Re: C1 indices
    (Original post by jessica_anne_clu)
    but how would you go about it? I know the answer is -1 but I don't know how you'd get it
    \dfrac12 = 2^{-1} \dfrac14 = ?
  11. thegodofgod's Avatar
    11 15-03-2012  19:03
    • TSR Legend
    • Location: London
    • Posts: 11,069
    Re: C1 indices
    (Original post by raheem94)
    e.g.

    2^{2x} = \frac12 2^{2x} = 2^{-1} 2x = -1 x = -\dfrac12
    x = -1, as

    4x = \frac{1}{4}
    Post rating:
    1
  12. raheem94's Avatar
    12 15-03-2012  19:04
    • TSR Demigod
    • Posts: 5,512
    Re: C1 indices
    (Original post by tnetennba)
    You could use logarithms:
    Log 4^x = Log 0.25
    x Log 4 = Log 0.25
    x= (Log 0.25)/(Log 4)
    x=-1
    OP is studying C1 indices, so she probably doesn't knows logarithms.
    Post rating:
    1
    1
  13. raheem94's Avatar
    13 15-03-2012  19:06
    • TSR Demigod
    • Posts: 5,512
    Re: C1 indices
    (Original post by thegodofgod)
    x = -1, as

    4x = \frac{1}{4}
    I didn't wanted to give the solution hence i was giving a similar example, i know the answer for OP's question is -1.
  14. thegodofgod's Avatar
    14 15-03-2012  19:06
    • TSR Legend
    • Location: London
    • Posts: 11,069
    Re: C1 indices
    (Original post by james.h)
    In this case, try multiplying both sides by 4:

    4^{x+1}=1

    Can you see the answer now?


    A general approach for any question like this involves logarithms, but I don't think they're covered in C1...?
    4^{x}=\frac{1}{4}

    2^{2x}=\frac{1}{4}

    2^{2x}=[\frac{1}{2}]^2

    2^{2x}=2^{-1 \times 2}

    2^{2x}=2^{-2}

    2x=-2

    x=-1
  15. jessica_anne_clu's Avatar
    15 15-03-2012  19:07
    • Respected Member
    • Location: Leicester
    • Posts: 161
    Re: C1 indices
    (Original post by raheem94)
    OP is studying C1 indices, so she probably doesn't knows logarithms.
    You're right I am studying C2 at the moment but I am retaking C1
  16. thegodofgod's Avatar
    16 15-03-2012  19:07
    • TSR Legend
    • Location: London
    • Posts: 11,069
    Re: C1 indices
    (Original post by raheem94)
    I didn't wanted to give the solution hence i was giving a similar example, i know the answer for OP's question is -1.
    My bad
  17. raheem94's Avatar
    17 15-03-2012  19:09
    • TSR Demigod
    • Posts: 5,512
    Re: C1 indices
    (Original post by thegodofgod)
    4^{x}=\frac{1}{4}

    2^{2x}=\frac{1}{4}

    2^{2x}=[\frac{1}{2}]^2

    2^{2x}=2^{-1 \times 2}

    2^{2x}=2^{-2}

    2x=-2

    x=-1
    Isn't it easier to do it in the below way:
    4^x = \dfrac14 4^x = 4^{-1} x=-1
    Involves only 2 steps.
  18. james.h's Avatar
    18 15-03-2012  19:11
    • Exalted and Worshipped Member
    • Posts: 1,065
    Re: C1 indices
    (Original post by thegodofgod)
    ...full solution...
    I did say "for any question". Try that method you've stated on something like a^x = 1/b :p:

    I get your point, though. :yep:
  19. thegodofgod's Avatar
    19 15-03-2012  19:14
    • TSR Legend
    • Location: London
    • Posts: 11,069
    Re: C1 indices
    (Original post by raheem94)
    Isn't it easier to do it in the below way:
    4^x = \dfrac14 4^x = 4^{-1} x=-1
    Involves only 2 steps.
    Hmm - didn't even notice that :giggle:

    Think it was a good decision of mine to drop maths after AS
  20. Dj.Clay's Avatar
    20 15-03-2012  19:22
    • Adored and Respected Member
    • Posts: 537
    Re: C1 indices
    Why would you convert everything to powers of 2 when it's already powers of 4? :/

    All you do for this question is rewrite 1/4 as 4^(-1) and compare indices.
Sign in to Reply
Search Thread
Advanced Search
Share this discussion:  
Useful resources

Articles:

Study Help rules and posting guidelinesStudy Help Member of the Month nominationsGuide to MathematicsMathematics resourcesMathematics websitesMathematics revision notes in the TSR wikiCambridge Assessment admissions tests (including STEP)How to use LaTeXCareers in Mathematics

Useful Dates:

Quick Link:

Unanswered Maths Threads

Groups associated with this forum:

View associated groups
Article updates
Moderators

We have a brilliant team of more than 60 volunteers looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is moderated by:

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

Shortcuts

Get Started

TSR Group

Using TSR

Info

Connect with TSR

Reputation gems:
The Reputation gems seen here indicate how well reputed the user is, red gem indicate negative reputation and green indicates a good rep.
Post rating score:
These scores show if a post has been positively or negatively rated by our members.