Question 433527
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.