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    (Original post by Pheylan)
    Use the substitution z = sinx to transform the differential equation

    cosx\frac{d^2y}{dx^2}+sinx\frac{  dy}{dx}-2ycos^3x=2cos^5x

    into the equation

    \frac{d^2y}{dz^2}-2y=2(1-z^2)

    here's what i've done so far:

    z=sinx
    \frac{dz}{dx}=cosx

    by the chain rule, \frac{dy}{dx}=cosx\frac{dy}{dz}

    \frac{d^2y}{dx^2}=cosx\frac{d^2y  }{dz^2}-sinx\frac{dy}{dz}

    cosx\frac{d^2y}{dx^2}=cos^2x\fra  c{d^2y}{dz^2}-sinxcosx\frac{dy}{dz}

    sinx\frac{dy}{dx}=sinxcosx\frac{  dy}{dz}

    so cos^2x\frac{d^2y}{dz^2}-sinxcosx\frac{dy}{dz}+sinxcosx\f  rac{dy}{dz}-2ycos^3x=2cos^5x

    cos^2x\frac{d^2y}{dz^2}-2ycos^3x=2cos^5x

    \frac{d^2y}{dz^2}-2ycosx=2cos^3x

    why the extra cosx on the last two terms :stomp:
    Retarded irrelevant question of the day: Is this Physics of Maths? :eek3:
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    (Original post by Pheylan)
    i'm not sure what that is but this is edexcel fp2 second order differential equations, quite a fun chapter

    Fun...Do you get these kind of questions in Physics? If so..Oh holy ******* **** **** ****..Save us! :eek:
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    (Original post by Pheylan)
    i don't think differential equations appear in a-level physics, and if they do they probably wouldn't ask you to do stuff like this question
    That reply truly enlightens me :o:
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    (Original post by Pheylan)
    haha, it really is fun though :yep:
    Equations are fun? They don't torture you into saying that do they? lol

    Maths has never really been my 'thing', i've always hated numbers. Evil little things which cause people to see bad grades on their exam papers...Its just fun in physics...Well, i was confident about physics until i saw a few threads
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    Ordinary differential equations comes up in UNIVERSITY LEVEL Physics, but not A-level Physics.
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    (Original post by Pheylan)
    lots of maths and numbers in physics but yeah, i used to think physics was fun too, can't stand it now
    Maths is fun and you can't stand Physics? :confused: Why is that?
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    (Original post by Pheylan)
    physics requires lots of thinking

    i don't like thinking
    What? Physics requires thinking and Maths doesn't it? Isn't maths like the most logical subject, thus requires the most thinking? :confused:

    Don't you find Physics exciting and fun? lol
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    (Original post by Pheylan)
    :nah:
    But why? Answer it! I might have a panic attack lol...So if you could go back would you not choose it as a subjet?
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    (Original post by Pheylan)
    i probably would, but only because it's the most mathsy subject after maths and further maths (that my sixth form offered)
    Uh..Mathsy? My physics era is officially over.
 
 
 
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