Question 433527: Use the "change of base" formula to find: log7 21
Answer by belle3833(46)   (Show Source):
You can put this solution on YOUR website! Change of Base Formula
logc(a)=logb(a)/logb(c)
b is the new base that we are changing it to. For our purposes (determining a decimal value), this new base can be either 10 or e.
For our particular example , c = 7and a = 21. We will first change to base 10. So b will be 10. This will give us
log7(21)=log10(21)/log10(7)
Plug this into your calculator to find the decimal value. 1.95
We could also choose to change to base e. This would give us c = 7 , a = 21, andb = e. We would get . You will see that when you plug this into your calculator, you will get thesame decimal answers as with the change to base 10.
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