Trigonometric derivative: power rule + product rule

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SUMMARY

The discussion focuses on deriving the function y = (cos{x}sin{2x})^{-2} using the power rule and product rule in calculus. The incorrect initial attempt led to a misunderstanding of the derivative, resulting in a different answer than the correct one, which is 4(3sin{2x} - 1) / (cos{2x}sin^{3}{2x}). The correct approach involves applying the product rule to find the derivative of cos{x}sin{2x} before applying the power rule.

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  • Familiarity with the power rule for differentiation.
  • Knowledge of the product rule for derivatives.
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cinematic
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Homework Statement


Derive the following:

y = (cosxsin2x)-2


2. The attempt at a solution

Basically I saw this as a power rule with two products in the middle.

So y = -2 (cos2cos2x-sinxsin2x)-1

But the correct answer is completely different, it's:

4(3sin2x - 1) all over
cos2xsin32x

Could someone please go through the steps to get to the correct solution? Thanks in advance!
 
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cinematic said:

Homework Statement


Derive the following:

y = (cosxsin2x)-22. The attempt at a solution

Basically I saw this as a power rule with two products in the middle.

So y = -2 (cos2cos2x-sinxsin2x)-1

But the correct answer is completely different, it's:

4(3sin2x - 1) all over
cos2xsin32x

Could someone please go through the steps to get to the correct solution? Thanks in advance!

y = (cos{x}sin{2x})^{-2}

\frac{dy}{dx} = -2(\cos{x}\sin{2x})^{-3}[\underbrace{\frac{d}{dx}(\cos{x}\sin{2x})}_{use\: product \:rule}]
 
Last edited:

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