If you're seeing this message, it means we're having trouble loading external resources for Khan Academy.
If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.
Introduction to logarithms
Learn how we define logarithms and use this definition in order to evaluate various logarithms. For example, evaluate log_2(8) as 3 by realizing that 2^3=8.
Sal explains what logarithms are and gives a few examples of finding logarithms.
Evaluate basic logarithmic expressions by using the fact that a^x=b is equivalent to log_a(b)=x.
Sal evaluates log_2(8), log_8(2), log_2(1/8), and log_8(1/2).
Evaluate advanced logarithmic expressions by using the fact that a^x=b is equivalent to log_a(b)=x.
Sal rewrites 100=10^2 as a logarithmic equation and log_5(1/125)=-3 as an exponential equation.
Given a few points on the graph of an exponential function, Sal plots the corresponding points on the graph of the corresponding logarithmic function.
Given incomplete tables of values of b^x and its corresponding inverse function, log_b(y), Sal uses the inverse relationship of the functions to fill in the missing values.
Solve various problems that focus on the relationship between a^x=b and log_a(b)=x.