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arrggh! newton-raphson nightmare, textbook mistakes?!?!

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Find the answers: Edexcel GCSE maths unofficial mark scheme 05-05-2016
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    the equation in question is 3sin(x+3)=cos(2x) to 4 dp between 0 =< x =< 7

    by rearranging the equation i get f(x) = 3sin(x+3)-cos(2x) which im sure is correct as this is what i get in maple and calculus bagatirx

    next step is to check by basically guess

    so I guess 3.5 which is -0.10854 and 3.75 is 1.0034 so i think ok jackpot I'm close enough

    anyway I differentiate it to 3COS(x+3) + 2sin(2x)

    I then calculator using general iteration formula which is xnew= x(-0.10854) - f(x)/f'(x)

    I run this continually until i get -0.1765 and this is what the newton-raphson calculator online confirms it as

    my book states the answer is 3.524 and 6.1067 I MEAN WTF IS THAT??!! is my answer wrong, am I doing something wrong?

    or is my book full of **** (which it has been lately, alot of stuff is incorrect but I can't rule it out that I haven't made a mistake or whether the fact the book is wrong)
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    I think there's a root at -0.1765, although that root isn't in the domain 0 ≤ x ≤ 7. I got 6.1067, but not 3.524. I don't understand how you can have two values, so I too am confused by your textbook. o.o
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    The book is correct mate. Go over your working again.
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    ok i figured it out, i was using the wrong value for x when it came to using the iteration formula
  5. Offline

    You need to do 3.5-F(3.5)/F'(3.5) to begin with. Then go from there.


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