Answer :
[tex]3a^2-9a-30โ[/tex]
Notice that all the terms are divisible by 3. First we factor out 3.
[tex]\begin{gathered} 3a2-9a-30โ \\ 3(a^2-3a-10) \end{gathered}[/tex]Also, the first two terms has a in it. We can factor out a.
[tex]\begin{gathered} 3(a^2-3a-10) \\ 3\lbrack a(a^{}-3)-10\rbrack \end{gathered}[/tex]Notice that we use the square bracket to indicate the distribution of the first factor which is 3, and the parenthesis indicates the distribution of the second factor a which only apply to the first two terms.
Answer:
[tex]3\lbrack a(a^{}-3)-10\rbrack[/tex]