## Precalculus (6th Edition) Blitzer

Please note that we have the following identity:$$\log_bMN=\log_bM+\log_bN$$So we have$$3\log_bx+3\log_by=3(\log_bx+\log_by)=3\log_b(xy)= \\ \log_b(xy)^3 \neq \log_b(x^3+y^3)$$(since $(xy)^3 \neq x^3+y^3$).