Answer
3
Work Step by Step
Step 1. Using the logarithm properties, we have $log_2[(x+1)(x-1)]=3$ which gives $x^2-1=2^3$
Step 2. Solving the equation, we have $x^2=9$ or $x=\pm3$
Step 3. Check the answers; we find only $x=3$ fits the original equation, while $x=-3$ is not in the domain.
