Rational Problem
- Thread starter Jason76
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D
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\(\displaystyle f'(x) = \dfrac{12}{x^{4}}\)].......................Is this actually f(x) and not f'(x)
\(\displaystyle f'(x) = 12x^{-4}\)
\(\displaystyle f'(x) = 48x^{-3}\)
Book says this is wrong.
If you REALLY started with
f(x) = 12*x-4
Then
f'(x) = (-4) * x-4-1
f'(x) = (-4) * x-5
Post Edited.
Ok understand.
Full problem:
\(\displaystyle f(x) = \dfrac{12}{x^{4}}\)
\(\displaystyle f'(x) = 12x^{-4}\)
\(\displaystyle f'(x) = 48x^{-5}\)
\(\displaystyle f'(x) = \dfrac{48}{x^{5}}\) - Answer
Last edited:
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HallsofIvy
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- Jan 27, 2012
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Are you paying attention?
It was
\(\displaystyle f(x) = \dfrac{12}{x^{4}}\)
\(\displaystyle f(x) = 12x^{-4}\)
\(\displaystyle f(x) = 12x^{-5}\)
\(\displaystyle f'(x) = \dfrac{48}{x^{5}}\)
Sorry.
Last edited:
HallsofIvy
Elite Member
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- Jan 27, 2012
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- 7,763
Good! No f' here.
You are still making the same mistake you have been told about before. The derivative of \(\displaystyle ax^n\) is \(\displaystyle nax^{n-1}\). What is "n" here?
Original Problem was negative. :shock:
Original Post edited to reflect change. But other mistake left in it.
\(\displaystyle f(x) = -\dfrac{12}{x^{4}}\)
\(\displaystyle f(x) = -12x^{-4}\)
\(\displaystyle f'(x) = (-4)(-12x^{-5})\)
\(\displaystyle f'(x) = 48x^{-5}\)
\(\displaystyle f'(x) = \dfrac{48}{x^{5}}\)
Original Post edited to reflect change. But other mistake left in it.
\(\displaystyle f(x) = -\dfrac{12}{x^{4}}\)
\(\displaystyle f(x) = -12x^{-4}\)
\(\displaystyle f'(x) = (-4)(-12x^{-5})\)
\(\displaystyle f'(x) = 48x^{-5}\)
\(\displaystyle f'(x) = \dfrac{48}{x^{5}}\)
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