A simple derivative that I'm messing up on

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SUMMARY

The derivative of the function f(x) = sin x + 2 cos^3 x is f'(x) = cos x - 6cos^2 x sin x. The initial mistake in the calculation involved incorrectly applying the power rule instead of the chain rule. The correct application of the chain rule, d/dx[f(g(x))] = f'(g(x))g'(x), clarifies the derivation of the sin x term in the final answer.

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  • Understanding of basic derivative properties
  • Familiarity with the chain rule in calculus
  • Knowledge of the power rule for derivatives
  • Ability to differentiate trigonometric functions
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  • Review the chain rule in calculus
  • Practice differentiating composite functions
  • Explore the power rule and its applications
  • Study trigonometric derivatives and their properties
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Students studying calculus, particularly those learning about derivatives and trigonometric functions, will benefit from this discussion.

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Homework Statement



Find f'(x) for f(x) = sin x + 2 cos^3 x

Homework Equations



Other than basic derivative properties and formulas, no.

The Attempt at a Solution



f'(x) = sin x + 2cos^3 x
= cos x - 6sin^2 x

The book says the answer is f'(x) = cos x - 6cos^2 x sin x however I don't understand where the sin x comes from... any help?
 
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Do you know the chain rule?
 
Yeah, d/dx[f(g(x))] = f'(g(x))g'(x). My bad, now I got the correct answer of f'(x) = cos x - 6cos^2 x sin x.. I think I used the power rule on 2cos^3 x by mistake before.
 

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