well this isn't a formal proof but...
means
so if is taken to a postive or negatve exponent will always be positive
example
"Explain why it is not possible to use the product law of logarithms to evaluate the expression log(-7) + log(-4)?"
I had a TIPS/Comm assignment yesterday, and i had this question. I didn't know how to answer it, except that you can't evaluate xlog(y) with y < 0 .. how would you guys do it?