Logarithmic differentiation:
$\displaystyle y = \ln(7)7^z \Leftrightarrow \ln(y) = \ln(\ln(7)7^z) = \ln\ln(7)+\ln(7)^z = \ln\ln(7)+z\ln(7) [/Math] [Math] \Rightarrow (\frac{1}{y})\frac{dy}{dx} = \ln{7} \Rightarrow \frac{dy}{dx} = \ln(7)y = \ln{7}\ln(7)7^z.$