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

    7
    ReputationRep:
    Okay so I'm having so much trouble trying to. Find the minimum value when we have an equation in the form Rcos(theta -alpha)
    One paper I do and the mark scheme says to equal this function to zero. Then I do another paper but this time it equals 1 to find minimum. Is there a method on trying to get these questions correct?


    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by Lilly1234567890)
    Okay so I'm having so much trouble trying to. Find the minimum value when we have an equation in the form Rcos(theta -alpha)
    One paper I do and the mark scheme says to equal this function to zero. Then I do another paper but this time it equals 1 to find minimum. Is there a method on trying to get these questions correct?


    Posted from TSR Mobile
    In general to find a maximum or minimum point of a function you have to differentiate it, then make it equal zero
    Offline

    16
    ReputationRep:
    (Original post by Lilly1234567890)
    Okay so I'm having so much trouble trying to. Find the minimum value when we have an equation in the form Rcos(theta -alpha)
    One paper I do and the mark scheme says to equal this function to zero. Then I do another paper but this time it equals 1 to find minimum. Is there a method on trying to get these questions correct?


    Posted from TSR Mobile
    I have just had a second to actually think about and use my brain to read the question, for these questions it's best to think about it graphically.

    On the normal cos graph, we know that maximum point is 1 and minimum point is at -1.

    We know then that if we do the transformation 2cos(x) (the same as doing 2f(x) where f(x) = cos(x)) that the maximum point would be 2 and minimum would be -2. So for Rcos(x) maximum would be R and minimum would be -R.

    Could you then use this to figure out the first place where Rcos(x-alpha) = -R ?
 
 
 
  • 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?
  • 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.