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    (Original post by qpqpqpqpqp)
    can someone explain 7ciii for june 2014 - i got y=tan75x which is wrong but i don't understand the mark scheme?
    i did cos^-1(-root3/2) = 150 = 2 theta, so theta = 75?
    further down in the ms it says condone 75
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    (Original post by qpqpqpqpqp)
    can someone explain 7ciii for june 2014 - i got y=tan75x which is wrong but i don't understand the mark scheme?
    i did cos^-1(-root3/2) = 150 = 2 theta, so theta = 75?
    (Original post by -jordan-)
    I've just done the same question and got the same thing
    That's because it isn't -root3/2. Your enlargement is scale factor root 12, so take out a factor of root 12 - cos2theta then equals -3/root12, etc
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    (Original post by Lau14)
    That's because it isn't -root3/2. Your enlargement is scale factor root 12, so take out a factor of root 12 - cos2theta then equals -3/root12, etc
    I got -3/root12, try and resolve that and you get the angle of 75 degrees.
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    (Original post by -jordan-)
    I got -3/root12, try and resolve that and you get the angle of 75 degrees.
    That is strange? (I did it in radians by accident earlier!)
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    (Original post by -jordan-)
    I got -3/root12, try and resolve that and you get the angle of 75 degrees.
    Ah no, nevermind, I see the problem - you have to look at both sin and cos and find the first common angle, which is 210 degrees - is this what the markscheme has?
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    I also got y=tan75x but the mark scheme only condones y=-tan75x?
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    (Original post by Lau14)
    Ah no, nevermind, I see the problem - you have to look at both sin and cos and find the first common angle, which is 210 degrees - is this what the markscheme has?
    Got it... but how do I find the common angle? Never seen a question like this before. Just assuming the angle is the same works for all the questions I've done has served me fine so far.
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    (Original post by -jordan-)
    Got it... but how do I find the common angle? Never seen a question like this before. Just assuming the angle is the same works for all the questions I've done has served me fine so far.
    You've gotten lucky a lot then!
    The same way as when you're trying to find multiple solutions to a trig equation, but with two of them. Write both down (sinx = and cosx = ) and find new solutions using 180-initial for sin and plus/minus or 360-initial for cos until you find a matching pair
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    (Original post by Lau14)
    You've gotten lucky a lot then!
    The same way as when you're trying to find multiple solutions to a trig equation, but with two of them. Write both down (sinx = and cosx = ) and find new solutions using 180-initial for sin and plus/minus or 360-initial for cos until you find a matching pair
    I just did this and got 150 as a pair?? Perhaps it's the signs messing me up?
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    (Original post by Rabadon)
    I just did this and got 150 as a pair?? Perhaps it's the signs messing me up?
    I swear I get a different answer every time I try and do this now! The method is to find the common angle, but I don't know what that is! (I really should look at the markscheme)
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    (Original post by Rabadon)
    I just did this and got 150 as a pair?? Perhaps it's the signs messing me up?
    Excuse my handwriting but here: https://www.dropbox.com/s/4hnt7u4988...09.38.png?dl=0 I think I got it figured out. I hadn't run into any problems like that before and I've managed to do most of the past papers...
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    (Original post by bartbarrow)
    Excuse my handwriting but here: https://www.dropbox.com/s/4hnt7u4988...09.38.png?dl=0 I think I got it figured out. I hadn't run into any problems like that before and I've managed to do most of the past papers...
    and so the penny drops! thank you!
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    (Original post by Lau14)
    I swear I get a different answer every time I try and do this now! The method is to find the common angle, but I don't know what that is! (I really should look at the markscheme)
    210 is the common angle.
    So y=tan(105)x
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    In which order do you multiply matrices?

    For example if i said find the matrix corresponding to the combined transformation of a reflection inthe line y ¼ x followed by a stretch parallel to the y-axis of scale factor 7.
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    (Original post by jake4198)
    In which order do you multiply matrices?

    For example if i said find the matrix corresponding to the combined transformation of a reflection inthe line y ¼ x followed by a stretch parallel to the y-axis of scale factor 7.
    If you are trying to find a matrix with order of transformations AB, you find the matrix BA (it's the reverse)
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    (Original post by jake4198)
    In which order do you multiply matrices?

    For example if i said find the matrix corresponding to the combined transformation of a reflection inthe line y ¼ x followed by a stretch parallel to the y-axis of scale factor 7.
    If you want to apply a transformation, say A and then you want to apply another one, say B then you multiply B by A to get the single matrix representing both.

    So you would multiply the stretch by the reflection
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    I'm having a dumb moment
    How do I make α^4+β^4 into the form only involving α+β αβ
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    (Original post by C0balt)
    I'm having a dumb moment
    How do I make α^4+β^4 into the form only involving α+β αβ
    I usually find a^2+b^2, square it and then take away the bits you don't need to get a^4 + b^4 on it's own, then it's easy substitution. Seems quicker than doing binomial expansion and then factorising it.
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    (Original post by -jordan-)
    I usually find a^2+b^2, square it and then take away the bits you don't need to get a^4 + b^4 on it's own, then it's easy substitution. Seems quicker than doing binomial expansion and then factorising it.
    My dumb. Moment is strong and I can't even do it
    wtf is wrong with me lmao
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    (Original post by -jordan-)
    I usually find a^2+b^2, square it and then take away the bits you don't need to get a^4 + b^4 on it's own, then it's easy substitution. Seems quicker than doing binomial expansion and then factorising it.
    Oh wait are you talking about this?
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