Derivative Substitution

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Jason
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\(In\,\,The\,\,Case\,\,Of\,\,Nested\,\,Functions:\)

\(\dfrac{dy}{dx} = [\dfrac{du}{dx}][\dfrac{dy}{du}]\)


\(ex\,\,a.\)

\(u = x^{2} - 4\)

\(\dfrac{du}{dx} = 2x\)

\(\dfrac{dy}{dx} = (u)^{3}\)


\(The\,\,Main\,\,Problem:\)

\(\dfrac{dy}{dx} = (x^{2} - 4)^{3} \)

\([\dfrac{du}{dx}][\dfrac{dy}{du}] =\)

\([2x][(3)(x^{2} - 4)^{3 - 1}] = \)

\(6x(x^{2} - 4)^{2} = \)

\(6x(x^{2} - 4)(x^{2} - 4) =\)

\(6x[2x^{2} - 4x^{2} - 4x^{2} + 16] = \)

\(6x[x^{4} - 8x^{2} + 16] =\)

\(6x^{5} - 48x^{3} + 96x\)


\(ex. b\)

\(u = 4x\)

\(\dfrac{du}{dx} = 4\)

\(\dfrac{dy}{du} = \cos(u) \)


\(The\,\,Main\,\,Problem\)

\(\dfrac{dy}{dx} = \sin(4x)\)

\([\dfrac{du}{dx}][\dfrac{dy}{du}] =\)

\([4][\cos(u)]\)

\(4\cos(4x)\)
 

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