If y = 3 cos 4x, dy/dx equals?
...If y = 3 cos 4x, dy/dx equals?
6 sin 8x
-24 sin 4x
12 sin 4x
-12 sin 4x
Correct answer is D
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
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