Question

d log[7](x)/dx

Answer 1

is this
\[\frac{d}{dx}\log_7(x)\]?

Answer 2

if so you get
\[\frac{1}{\ln(7)x}\]

Answer 3

change of base tells you that
\[\log_7(x)=\frac{\ln(x)}{\ln(7)}\] take the derivative and get the answer above