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Curves and Tangents.....Differentiation thingymabob - HSN forum

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Curves and Tangents.....Differentiation thingymabob


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#1 lynnie

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Posted 24 September 2006 - 08:14 PM

Ok..well to be honest im too scared to say to my teacher that I do not understand a thing that comes from her mouth when she is talking maths mumble jumble...apart from that, she is a lovely woman.

Ok well we've been filed with some homework...and I'm just....LOST!
And was hopind I could get some extra help off of here to help me to understand how to do these questions. Thanks!

Ok well...here's a question from my H/W

1. A curve has equation y= -x^4 + 4x^3 -2
(a) Find the coordinates of the stationary points
(b) Determine their nature

I will appreciate any help. Thanks again.

P.S I may need help with others later. x

#2 Nathan

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Posted 24 September 2006 - 10:59 PM

$$
f(x) = x^4  + 4x^3  - 2
$$

$$
f'(x) = 4x^3  + 12x^2 
$$
and solve thus;

x=-3; x=0

then;
when x=-3; f(x) = -29
when x=0; f(x) = -2....therefore stationary points occur at (-3, -29) and (0,-2)

to find the nature of the points, it is best to do a nature table (as shown)


and that;s how you do it...iirc =$

Attached Thumbnails

  • Attached Image: graph1.jpg
  • Attached Image: nature_table.JPG


#3 dfx

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Posted 24 September 2006 - 11:11 PM

By the way, if she's lovely, it might be worth a stab telling her you don't understand. smile.gif





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