Question

3^a = 7^b = 21^c, express a in terms of b and c
Can someone pls help me

Answer 1

use logarithms. you will need to deal with them separately.
You take a log of both sides (doesn't matter what log base you use, say base 10 or base e)
Then use the rule log(a^n) = n log(a) - so the power gets taken outside of the log

\[3^a = 7^b\]
\[\log(3^a) = \log(7^b)\]
\[a \log(3) = b \log(7)\]
\[a = \frac{ b \log(7) }{ \log(3) }\]

Try this for 3^a = 21^c

Answer 2

I get the idea but how can i get d solution from the question. The answer given for this question is a=(bc/ b-c)