What is log675 with base 5 × log 3 with base 3? We have to calculate (log 675 to the base 5) × (log 3 to the base 3)
Note the following important points :
(1.) log 675 to the base 5
=> log 675 to the base ‘e’ / log 5 to the base ‘e’
=> ln 675 / ln 5
Since 675 = 5^2 × 3^3
=> ln 675 = ln [5^2 × 3^3]
=> ln (5^2) + ln (3^3)
=> 2 ln 5 + 3 ln 3
Hence, log 675 to the base 5
= ln 675 / ln 5
= [2ln 5 + 3ln 3] / ln 5
(2.) Similarly, log 3 to the base 3
=> Since the logarithm of any natural number 'x' to the base of same number 'x' is always 1 (since any natural number raised to the power '1′ is equal to the same number) ,
Thus, (log 3 to the base 3) = 1
Hence, our problem reduces to:
(log 675 to the base 5) × (log 3 to the base 3)
=> [(2ln 5 + 3ln 3) / ln 5] × (1)
=> (2ln 5 + 3ln 3) / ln 5
=> So we only require the values of natural logarithm of 3 and 5 :)
We should remember these values, or we can always use log table.
