Undoing Exponential Functions Logarithms are how we undo exponential functions. The base of the logarithm is also the base of the exponent. However, logarithms give you the exponent as their output. So if we have log a = c then that means b = a 1. What is the value of y in each of the following? First, rewrite as an exponential expression. Then solve for y. a. logy = 8 b. log,y = 3 c. logy = 0 2. Is it ever possible for a logarithm to equal a negative number (ex log,y=-4)? Why or why not? 3. First rewrite the following logarithms as exponential expressions. Then, without a calculator, solve the logarithm. a. log,64 b. log,81 c. 109 125