Find the derivative of LaTeX: \displaystyle y = \frac{\left(1 - 9 x\right)^{6} \left(- 7 x - 7\right)^{2} e^{x} \cos^{4}{\left(x \right)}}{\left(9 x + 4\right)^{3} \sqrt{\left(x + 7\right)^{3}}}

Taking the natural logarithm of both sides of the equation and expanding the right hand side gives: LaTeX: \ln(y) = \ln{\left(\frac{\left(1 - 9 x\right)^{6} \left(- 7 x - 7\right)^{2} e^{x} \cos^{4}{\left(x \right)}}{\left(9 x + 4\right)^{3} \sqrt{\left(x + 7\right)^{3}}} \right)} Expanding the right hand side using the product and quotient properties of logarithms gives: LaTeX: \ln(y) = x + 6 \ln{\left(1 - 9 x \right)} + 2 \ln{\left(- 7 x - 7 \right)} + 4 \ln{\left(\cos{\left(x \right)} \right)}- \frac{3 \ln{\left(x + 7 \right)}}{2} - 3 \ln{\left(9 x + 4 \right)} Taking the derivative on both sides of the equation yields: LaTeX: \frac{y'}{y} = - \frac{4 \sin{\left(x \right)}}{\cos{\left(x \right)}} + 1 - \frac{27}{9 x + 4} - \frac{3}{2 \left(x + 7\right)} - \frac{14}{- 7 x - 7} - \frac{54}{1 - 9 x} Solving for LaTeX: \displaystyle y' and substituting out y using the original equation gives LaTeX: y' = \left(- \frac{4 \sin{\left(x \right)}}{\cos{\left(x \right)}} + 1 - \frac{27}{9 x + 4} - \frac{3}{2 \left(x + 7\right)} - \frac{14}{- 7 x - 7} - \frac{54}{1 - 9 x}\right)\left(\frac{\left(1 - 9 x\right)^{6} \left(- 7 x - 7\right)^{2} e^{x} \cos^{4}{\left(x \right)}}{\left(9 x + 4\right)^{3} \sqrt{\left(x + 7\right)^{3}}} \right) Using some Trigonometric identities to simplify gives LaTeX: y' = \left(- 4 \tan{\left(x \right)} + 1 - \frac{14}{- 7 x - 7} - \frac{54}{1 - 9 x}- \frac{27}{9 x + 4} - \frac{3}{2 \left(x + 7\right)}\right)\left(\frac{\left(1 - 9 x\right)^{6} \left(- 7 x - 7\right)^{2} e^{x} \cos^{4}{\left(x \right)}}{\left(9 x + 4\right)^{3} \sqrt{\left(x + 7\right)^{3}}} \right)