# SOLUTION: Evaluate the logarithmic expression 1-log[5]21

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 Click here to see ALL problems on Exponential-and-logarithmic-functions Question 278554: Evaluate the logarithmic expression 1-log[5]21Answer by jsmallt9(3296)   (Show Source): You can put this solution on YOUR website!If the problem is: then, since no calculator I know "knows" base 5 logrithms, we need to convert this logarithm to a base our calculator does "know", like base 10 or base e (ln). There is a base conversion formula for this: Using this to convert the base 5 logarithm into a base 10 logarithm we get: Now you can use your calculators to find the two logarithms, divide them and then subtract that from 1. (Be sure to use this order. Do not divide 21 by 5 first and then find the logarithm. That will not give you the correct answer.)