** Final Answer

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** Step-by-step Solution **

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Apply the quotient rule for differentiation, which states that if $f(x)$ and $g(x)$ are functions and $h(x)$ is the function defined by ${\displaystyle h(x) = \frac{f(x)}{g(x)}}$, where ${g(x) \neq 0}$, then ${\displaystyle h'(x) = \frac{f'(x) \cdot g(x) - g'(x) \cdot f(x)}{g(x)^2}}$

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$\frac{\frac{d}{dx}\left(\left(x^5+3x\right)^4\right)\cos\left(x\right)-\left(x^5+3x\right)^4\frac{d}{dx}\left(\cos\left(x\right)\right)}{\cos\left(x\right)^2}$

Learn how to solve problems step by step online. Find the derivative of d/dx(((x^5+3x)^4)/cos(x)). Apply the quotient rule for differentiation, which states that if f(x) and g(x) are functions and h(x) is the function defined by {\displaystyle h(x) = \frac{f(x)}{g(x)}}, where {g(x) \neq 0}, then {\displaystyle h'(x) = \frac{f'(x) \cdot g(x) - g'(x) \cdot f(x)}{g(x)^2}}. The power rule for differentiation states that if n is a real number and f(x) = x^n, then f'(x) = nx^{n-1}. The derivative of the cosine of a function is equal to minus the sine of the function times the derivative of the function, in other words, if f(x) = \cos(x), then f'(x) = -\sin(x)\cdot D_x(x). Any expression multiplied by 1 is equal to itself.

** Final Answer

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