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    In the Edexcel textbook, when you are asked to find the equation of a tangent/normal to an ellipse, the answers in the back use formulae that isn't in the formula booklet. They have been proven in the examples before the exercises. Is this suggesting that these formulae ought to be memorised in the exam or are you only credited for fully working out the first derivative and using y-y1=m(x-x1)?

    Similarly, they prove a condition that must be satisfied for a line to be tangent to an ellipse. Is this meant to be memorised also?
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    (Original post by BasicMistake)
    In the Edexcel textbook, when you are asked to find the equation of a tangent/normal to an ellipse, the answers in the back use formulae that isn't in the formula booklet. They have been proven in the examples before the exercises. Is this suggesting that these formulae ought to be memorised in the exam or are you only credited for fully working out the first derivative and using y-y1=m(x-x1)?

    Similarly, they prove a condition that must be satisfied for a line to be tangent to an ellipse. Is this meant to be memorised also?
    you mean things like the condition for a line being tangent to an eclipse being  \displaystyle b^2 + a^2m^2 = c^2 etc, if so then you can either learn them off (advised, as itll save you lots of time in the exams) or just derive them in the exam
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    (Original post by DylanJ42)
    you mean things like the condition for a line being tangent to an eclipse being  \displaystyle b^2 + a^2m^2 = c^2 etc, if so then you can either learn them off (advised, as itll save you lots of time in the exams) or just derive them in the exam
    Yes, that's the one.

    The other two are:
    Tangent
     \displaystyle aysin\theta + bxcos\theta = ab
    Normal
     \displaystyle bycos\theta - axsin\theta = (b^2-a^2) sin\theta cos\theta

    So you can just sub in values into these formulae and you'll still get full method marks in the exam?
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    (Original post by BasicMistake)
    Yes, that's the one.

    The other two are:
    Tangent
     \displaystyle aysin\theta + bxcos\theta = ab
    Normal
     \displaystyle bycos\theta - axsin\theta = (b^2-a^2) sin\theta cos\theta

    So you can just sub in values into these formulae and you'll still get full method marks in the exam?
    I just had a look at the book and I dont think you could quote that. However Id assume if you had to use it you would be asked to derive it in part (a), and then maybe apply it in a part b or something.
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    (Original post by DylanJ42)
    I just had a look at the book and I dont think you could quote that. However Id assume if you had to use it you would be asked to derive it in part (a), and then maybe apply it in a part b or something.
    Ah okay. Thanks for your help!
 
 
 
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