Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    Hey mighty TSR math forum

    I need to retake C2 soon. My logs are sluggish right now, i need to change that! :teeth: here is the question (Btw I have the laws in my head, i just need a push in the right direction):


    Solve 5^(2x) - 12[5^x] + 35 = 0

    I get mixed up with these. I can do the simple logs fine!

    Thanks!
    Offline

    18
    ReputationRep:
    If I rewrite 5^(2x) as (5^x)^2, does that help?

    Further hint (only open once you've thought about it):

    Spoiler:
    Show
    No really, think about it!
    Spoiler:
    Show
    Let u = 5^x
    Offline

    0
    ReputationRep:
    5^2x = 5^x x 5^x

    Can you see the quadratic?
    • Thread Starter
    Offline

    2
    ReputationRep:
    right. I got it!!

    I did try (5^x)^2 before.

    Now i see it!

    you eventually get (x-5)(x-7)

    I feel less of a crazy scientist now

    Is there a rule with these though? Say there wasnt a 5^(2x) but say a 4^(2x) how would you use logs to solve a ******* like this?
    Offline

    18
    ReputationRep:
    (Original post by yurihammo)
    Is there a rule with these though? Say there wasnt a 5^(2x) but say a 4^(2x) how would you use logs to solve a ******* like this?
    In the 4^(2x) case, it's just (4^x)^2...

    And no, you don't get (x-5)(x-7) = 0, you get (u - 5)(u - 7) = 0, which you then need to solve for u and THEN solve for x.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: September 26, 2010

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
Poll
How are you feeling in the run-up to Results Day 2018?
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

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

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