Cho

- Hướng dẫn giải

$$\begin{gathered} {\left(3a-5b\right)}^2=9a^2+25b^2-30ab \\ \begin{array}{l}=25a^2+9b^2-30ab-16\left(a^2-b^2\right)\\ ={\left(5a\right)}^2+{\left(3b\right)}^2-2.\left(5a\right)\left(3b\right)-16.4c^2\\ ={\left(5a-3b\right)}^2-{\left(8c\right)}^2\\ =\left(5a-3b-8c\right)\left(5a-3b+8c\right)\end{array} \end{gathered}$$