Hello from MrBillDoesMath!
Answer:
(1/x) * ( (1/ln7) - (1/ln9) )
Discussion:
Using the change of base formula
log_b(x) = ln(x) / ln(b) sp where _b means to log to base b
f(x) = ln(x)/ln(7) - ln(x)/ln(9)
so
f' = (1/x) *(1/ln7) - (1/x) *(1/ln9)
= (1/x) * ( (1/ln7) - (1/ln9) )
Thank you,
MrB
