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    I know you have to use simultaneous equation, but I have no idea where to start. I don't think we've even covered this in class. Could anyone give me some hints on how I go about answering this question?
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    (Original post by Mystelle)
    I know you have to use simultaneous equation, but I have no idea where to start. I don't think we've even covered this in class. Could anyone give me some hints on how I go about answering this question?
    This is quite a unique question. I decided to do it by substituting one into the other.

    I started by rewriting the x equation in terms of \cos\theta using the double angle formulae, then rearranging the y equation for \cos\theta. You can then do some substitution to get it just in terms of y
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    (Original post by Ed5)
    This is quite a unique question. I decided to do it by substituting one into the other.

    I started by rewriting the x equation in terms of \cos\theta using the double angle formulae, then rearranging the y equation for \cos\theta. You can then do some substitution to get it just in terms of y
    Is this C3 or C4?
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    (Original post by Mystelle)
    Is this C3 or C4?
    it's c3 trig identities
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    sin(theta)/cos(theta) = ta(theta)
    iirc
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    (Original post by Mystelle)
    Is this C3 or C4?
    If you're on edexcel it's C3

    The one you're looking for is \cos(a+b)=\cos{a}\cos{b} - \sin{a}\sin{b}

    So when you shove in 2\theta it becomes \cos(\theta+\theta)=\cos^2{ \theta }-\sin^2{\theta}
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    So ****ing happy I stopped doing Maths after High School.
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    (Original post by Ed5)
    If you're on edexcel it's C3

    The one you're looking for is \cos(a+b)=\cos{a}\cos{b} - \sin{a}\sin{b}

    So when you shove in 2\theta it becomes \cos(\theta+\theta)=\cos^2{ \theta }-\sin^2{\theta}
    Actually for Edexcel this would be C4 since it would come under the category of "parametric equations". You wouldn't see it in C3.
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    (Original post by Notnek)
    Actually for Edexcel this would be C4 since it would come under the category of "parametric equations". You wouldn't see it in C3.
    Yeah I was wondering where Parametric to Cartesian conversion came from... is there any way to tackle this question using C3 knowledge?
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    (Original post by Mystelle)
    Yeah I was wondering where Parametric to Cartesian conversion came from... is there any way to tackle this question using C3 knowledge?
    Yes. It will just be harder especially if this is the first one of these types of questions that you've done.

    I recommend aiming to get both right-hand-sides in terms of \cos \theta only i.e. you can't have \cos 2\theta or \sin \theta etc.

    Do you know the three forms of the identity for \cos 2\theta? One of them only has \cos \theta in it.
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    (Original post by Mystelle)
    Yeah I was wondering where Parametric to Cartesian conversion came from... is there any way to tackle this question using C3 knowledge?
    Out of interest, why are you doing C4 questions if you haven't learnt C4 yet?
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    (Original post by King Leonidas)
    So ****ing happy I stopped doing Maths after High School.
    How do you sleep at night knowing that there is so much mathematics that you haven't explored?
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    (Original post by Notnek)
    Out of interest, why are you doing C4 questions if you haven't learnt C4 yet?
    This was in my homework, as are a couple of C4 reverse chain rule questions, which we have been taught in class. But we've never gone through this sort of question before.

    The only identities for cos(2theta) I know of are cos^(2)theta - sin^(2)theta, 2cos^(2)theta - 1 and 1 - 2sin^(2)theta.
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    (Original post by Notnek)
    How do you sleep at night knowing that there is so much mathematics that you haven't explored?
    Just fine, as long as I can count that's the main thing

    Learning all those equations and symbols just seems mundane, and only a necessity for a career, which would require use of it.

    Prepare your angus for this controversial comment:
    Spoiler:
    Show
    I don't need Maths to live a fruitful life
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    (Original post by Mystelle)
    This was in my homework, as are a couple of C4 reverse chain rule questions, which we have been taught in class. But we've never gone through this sort of question before.

    The only identities for cos(2theta) I know of are cos^(2)theta - sin^(2)theta, 2cos^(2)theta - 1 and 1 - 2sin^(2)theta.
    The second one is what you need since this is only in terms of \cos \theta. So you have

    x=2\cos^2 \theta - 1

    Now get y in terms of only \cos \theta. Then think about how you can eliminate the \cos \theta variable so you have an equation containing only x and y.

    Ask if you still need help - don't worry if you can't do it since this type of question is new to you.
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    (Original post by King Leonidas)
    Just fine, as long as I can count that's the main thing

    Learning all those equations and symbols just seems mundane, and only a necessity for a career, which would require use of it.

    Prepare your angus for this controversial comment:
    Spoiler:
    Show

    I don't need Maths to live a fruitful life
    I was being facetious - of course you don't need A Level maths GCSE maths is all you need for the vast majority of careers.
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    (Original post by Notnek)
    I was being facetious - of course you don't need A Level maths GCSE maths is all you need for the vast majority of careers.
    Just stared at your avatar for a minute straight, now my head hurts
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    (Original post by King Leonidas)
    Just stared at your avatar for a minute straight, now my head hurts
    Then I recommend having some pills ready if you decide to click on this link.
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    (Original post by Notnek)
    Then I recommend having some pills ready if you decide to click on this link.
    Dude, not cool

    Seriously, I think you just gave me Epilepsy.
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    (Original post by Notnek)
    The second one is what you need since this is only in terms of \cos \theta. So you have

    x=2\cos^2 \theta - 1

    Now get y in terms of only \cos \theta. Then think about how you can eliminate the \cos \theta variable so you have an equation containing only x and y.

    Ask if you still need help - don't worry if you can't do it since this type of question is new to you.
    Thank you for breaking this down for me. Could you please check if the solution I reached is correct?

    Attachment 691478
 
 
 
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