# What is the answer for question 15) ? http://postimg.org/image/6g52noj6f/

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The Product Rule for Logarithms

For any positive numbers M, N and `a (a=1)` ,

`log_aMN = log_aM + log_aN`

It is not possible to use the product rule for logarithms on log(-7) + log(-4), since -7 anf -4 are not positive numbers.