Question

Write 1-2log7^x as a single logarithm

Answer 1

2log(7^x) = log(7^(2x))
1 can be written as log(10)
1-2log7^x = log(10) - log(7^(2x))
Then you can combine the logs using the identity:
log(A) - log(B) = log(A/B)