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

    2
    ReputationRep:
    Hi, i have another C3 question. Its on another topic so i started another thread (If that is that ok?)
    https://7c95ed1f832973eac0c6e1a52b08...20C3%20OCR.pdf
    Im an extremely lost on question 9(iii).
    I looked at the market scheme and it said to "Attempt to relate k to at least 2 6sin 30".
    I Cant see how this would help?
    Thanks in advance.

    Offline

    22
    ReputationRep:
    (Original post by SamuelN98)
    Hi, i got another C3 question. Its on another topic so i started another thread (Is that ok?)
    I'm glad that you started another thread.

    https://7c95ed1f832973eac0c6e1a52b08...20C3%20OCR.pdf
    Im an extremely lost on question 9(iii).
    I looked at the market scheme and it said to "Attempt to relate k to at least 2 6sin 30".
    Cant see how this would help?
    Can you see (i) of the question? Multiply through by 6 and compare the RHS. (the angles have to be divided by 1/3 as well)

    We get k = 6\sin^2 \frac{\theta}{3}.

    You know that since \theta is bounded between -90 and +90 then we have \frac{\theta}{3} being bounded by -30 and +30.

    So \sin \frac{\theta}{3} is bounded between -1/2 and +1/2.

    So \sin^2 \frac{\theta}{3} is bounded between 0 and 1/4.

    So k = 6\sin^2 \frac{\theta}{3} is bounded between...?
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by Zacken)
    I'm glad that you started another thread.



    Can you see (i) of the question? Multiply through by 6 and compare the RHS. (the angles have to be divided by 1/3 as well)

    We get k = 6\sin^2 \frac{\theta}{3}.

    You know that since \theta is bounded between -90 and +90 then we have \frac{\theta}{3} being bounded by -30 and +30.

    So \sin \frac{\theta}{3} is bounded between -1/2 and +1/2.

    So \sin^2 \frac{\theta}{3} is bounded between 0 and 1/4.

    So k = 6\sin^2 \frac{\theta}{3} is bounded between...?
    So, that gives the upper bound of 3/2 , how do you get the lower bound?
    Offline

    22
    ReputationRep:
    (Original post by SamuelN98)
    So, that gives the upper bound of 3/2 , how do you get the lower bound?
    0.

    0 * 6 is still 0.
 
 
 
  • 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
    Brexit voters: Do you stand by your vote?
    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

    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.