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OCR (not MEI) C2 - Wednesday 20th May 2015 Watch

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    y^2= 27
    log3(y^2)= log3(27)
    2log3(y) = log3(3) + log3(3) + log3(3) *move power of y in front of log
    * 27= 3x3x3 so break apart using log rules
    2log3(y) = 3 *loga(a) =1
    log3(y)= 3/2
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    What happens when you are doing trigonometry and you get a negative angle ?
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    (Original post by Kadak)
    What happens when you are doing trigonometry and you get a negative angle ?
    Do you have a question as an example?
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    (Original post by Kadak)
    Where did you get the 272 or the log after it ?
    Sorry I forgot to press enter :P,
    y²=27
    log3y² = log327
    2log3y = 3
    log3y = 1.5
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    https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
    Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
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    (Original post by Kadak)
    https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
    Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
    use cast diagram to find the positive angle then keep going like a normal question like this
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    Quick question ?Do we have to show the CAST diagram ?Can we draw two ,one for each angle Im finding ?
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    (Original post by Kadak)
    https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
    Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
    That is no problem. Can you please give me a min to write it up
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    Can anyone help me with this log question please?

    Find the roots of the equation 2log(base4)x - log(base4)(-7x+3)=-1/2?

    I have got to 2x^2 + 7x - 3 = 0 but you have to use the quadratic formula to factorise this and I do not get the correct answer...have I made a mistake?

    Thanks!
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    (Original post by Kadak)
    https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
    Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
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    (Original post by Issy :))
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    I use the CAST method . Im confused ,I thought we woud add 180 to 19.5.For the engative angle,did you substract from 180 ?
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    (Original post by Kadak)
    I use the CAST method . Im confused ,I thought we woud add 180 to 19.5.For the engative angle,did you substract from 180 ?
    Do you have the answers? I have been doing maths all day so might have messed it up. My brain is literally fried.
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    https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
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    (Original post by giantbecky)
    Can anyone help me with this log question please?

    Find the roots of the equation 2log(base4)x - log(base4)(-7x+3)=-1/2?

    I have got to 2x^2 + 7x - 3 = 0 but you have to use the quadratic formula to factorise this and I do not get the correct answer...have I made a mistake?

    Thanks!
    I got that equation as well, can you tell what paper this question is from.
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    (Original post by Sahil_)
    I got that equation as well, can you tell what paper this question is from.
    It's not from a paper, it's from this revision guide/textbook...I can tell you the answers if you want?
    I thought maybe the answers were wrong but when I put them back into the original log equation they give -1/2
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    No, I was right, I just got fed up writing out all the answers halfway through. I really can't explain the cast method as I have always been taught the graph way. Let me think a mo and see if I can explain it
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    (Original post by giantbecky)
    It's not from a paper, it's from this revision guide/textbook...I can tell you the answers if you want?
    I thought maybe the answers were wrong but when I put them back into the original log equation they give -1/2
    If you put the answers from the textbook into the equation does is also give -1/2?
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    Ok, so the 19.5 value is positive so can only be in the first and second quadrant yes (CAST so only A and S) therefore is 180-19.5.
    The negative value, for sin to be negative it must be in the 3rd or 4th quadrant. Therefore, ignore the negative when typing into the calc then do 360-23.6 and 180+23.6
    That is using the cast diagram (needed a min to jog my memory of the method)

    (Original post by Kadak)
    I use the CAST method . Im confused ,I thought we woud add 180 to 19.5.For the engative angle,did you substract from 180 ?
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    (Original post by Sahil_)
    If you put the answers from the textbook into the equation does is also give -1/2?
    the answers are 3 and 1/2 and actually I just tried 1/2 and I don't think that works as -7x1/2 +3 = -1/2 and you can't take logs of negative numbers...

    So maybe the textbook is wrong?
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    (Original post by Issy :))
    Ok, so the 19.5 value is positive so can only be in the first and second quadrant yes (CAST so only A and S) therefore is 180-19.5.
    The negative value, for sin to be negative it must be in the 3rd or 4th quadrant. Therefore, ignore the negative when typing into the calc then do 360-23.6 and 180+23.6
    That is using the cast diagram (needed a min to jog my memory of the method)
    Thank you so much !
 
 
 
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