Turn on thread page Beta
    • Thread Starter
    Offline

    10
    ReputationRep:
    I know how to do every part, apart from part C) where it asks to find t
    Attached Images
     
    • Community Assistant
    • Study Helper
    Offline

    20
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by chrlhyms)
    I know how to do every part, apart from part C) where it asks to find t
    Ah the ferris wheel question - a very common question in the maths forum

    You say you can't find t but does that mean you've already found the maximum value of H? Please post all your working / thoughts.
    Offline

    16
    ReputationRep:
    Try rewriting the H equastion in th Rcos ("") form and then think about ways you can maximise your H value
    Offline

    15
    ReputationRep:
    (Original post by chrlhyms)
    I know how to do every part, apart from part C) where it asks to find t
    what a classic, i remember i struggled on this , now if i remember.

    The max value of H means to make H as big as possible.

    So what can you do to the cos thing you now got from part a to make H as big as possible?
    Set it equal to 0? -1? or 1? what gives you the biggest value of H
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Notnek)
    Ah the ferris wheel question - a very common question in the maths forum

    You say you can't find t but does that mean you've already found the maximum value of H? Please post all your working / thoughts.
    So i've found H as 10 + root(85)
    and the equation of H as

    H=10-root85 cos(pit/5 +0.2187)
    but cant think how I would find the maximum value of t as surely this would be 1 but the MS says -1?
    • Community Assistant
    • Study Helper
    Offline

    20
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by chrlhyms)
    So i've found H as 10 + root(85)
    and the equation of H as

    H=10-root85 cos(pit/5 +0.2187)
    but cant think how I would find the maximum value of t as surely this would be 1 but the MS says -1?
    If cos(pit/5 +0.2187) = 1 then

    10-root85 cos(pit/5 +0.2187) = 10 - root85

    But you said the maximum was 10 + root85 so cos(pit/5 +0.2187) must be -1.
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Notnek)
    If cos(pit/5 +0.2187) = 1 then

    10-root85 cos(pit/5 +0.2187) = 10 - root85

    But you said the maximum was 10 + root85 so cos(pit/5 +0.2187) must be -1.
    Sorry, I still dont understand!
    • Community Assistant
    • Study Helper
    Offline

    20
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by chrlhyms)
    Sorry, I still dont understand!
    How did you find that the maximum value of H is 10 + root(85)? Please explain fully.
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Notnek)
    How did you find that the maximum value of H is 10 + root(85)? Please explain fully.
    well since the original equation was stretched by a factor of root 85, the new equation was +10 onto that, therefore the new maximum was 10 + root85 and minimum 10-root85
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Notnek)
    If cos(pit/5 +0.2187) = 1 then

    10-root85 cos(pit/5 +0.2187) = 10 - root85

    But you said the maximum was 10 + root85 so cos(pit/5 +0.2187) must be -1.
    if cos(pit/5) +0.2187)=-1
    then surely 10-root85 cos(pit/5) +0.2187)= -10+root85
    which isnt the max?
    • Community Assistant
    • Study Helper
    Offline

    20
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by chrlhyms)
    if cos(pit/5) +0.2187)=-1
    then surely 10-root85 cos(pit/5) +0.2187)= -10+root85
    which isnt the max?
    I'll write it using brackets to make it clearer:

    \displaystyle H = 10-\left[\sqrt{85} \cos\left(\frac{\pi t}{5} +0.2187\right)\right]

    So when

    \displaystyle \cos\left(\frac{\pi t}{5} +0.2187\right) = -1

    you get

    \displaystyle H = 10 - \left[\sqrt{85} \times -1\right] = 10 - [-\sqrt{85}] = 10 + \sqrt{85}
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Notnek)
    I'll write it using brackets to make it clearer:

    \displaystyle H = 10-\left[\sqrt{85} \cos\left(\frac{\pi t}{5} +0.2187\right)\right]

    So when

    \displaystyle \cos\left(\frac{\pi t}{5} +0.2187\right) = -1

    you get

    \displaystyle H = 10 - \left[\sqrt{85} \times -1\right] = 10 - [-\sqrt{85}] = 10 + \sqrt{85}
    perfect! I understand now thank you! that question was horrible
    • Community Assistant
    • Study Helper
    Offline

    20
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by chrlhyms)
    perfect! I understand now thank you! that question was horrible
    Yes it was a bit nasty. They've asked a ferris wheel type question a few times in C3 exams so it's worth practicing them
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by Notnek)
    Yes it was a bit nasty. They've asked a ferris wheel type question a few times in C3 exams so it's worth practicing them
    at least now i will know how to solve it! thank you!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: October 21, 2017
Poll
Could you cope without Wifi?
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.