expand:
log base 7 a/5

condense:
g log 7

solve:
log base 7 5=1/3log base 7 (x-1)

approximate using the change of base formula (to two decimal places):
log base 3 13=?

There are a few formulas regarding loagarithms that you need to memorize:


log_c(a*b) = log_c(a) + log_c(b) \\
log_c(a/b) = log_c (a) - log_c(b) \\
log_c (a^b) = b * log_c(a) \\
log_c(a) = log_c(b) * log_b(a)



With these facts you can solve all the problems you posted. I'll help you with the first - use the second formula above, setting b = 5.

Thank you so much!