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If y = 3 cos 4x, dy/dx equals?

Mathematics
JAMB 2009

If y = 3 cos 4x, dy/dx equals?

  • A. 6 sin 8x
  • B. -24 sin 4x
  • C. 12 sin 4x
  • D. -12 sin 4x
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Correct Answer: Option D
Explanation

y = 3 cos 4x

Applying product rule:

\(\frac{dy}{dx}\) = u\(\frac{dv}{dx}\) + v\(\frac{du}{dx}\)

Where u = 3 and v = cos 4x

\(\frac{du}{dx}\) of 3 = 0 and 

\(\frac{dv}{dx}\) of cos 4x = -4sin 4x


\(\frac{dy}{dx}\) = 3 \(\times\) -4 sin 4x  +   cos 4x \(\times\) 0

\(\frac{dy}{dx}\) = -12 sin 4x
 

There is an explanation video available below.


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Explanation Video

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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
NECO June/July 2024 - Get offline past questions & answers - Download objective & theory, all in one app 48789
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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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NECO June/July 2024 - Get offline past questions & answers - Download objective & theory, all in one app 48789