Solution
Factor the following equations by product and sum.
Then determine the solutions
[tex]a^2-121=0[/tex]
Step 1: Difference of two square
[tex]\begin{gathered} a^2-121=0 \\ a^2-11^2=0 \\ (a-11)(a+11)=0 \end{gathered}[/tex]
Therefore the correct answer is
[tex](a-11)(a+11)[/tex]
Step 2: Then the solutions are
[tex]\begin{gathered} a-11=0,a+11=0 \\ a=11,a=-11 \\ a=\pm11 \end{gathered}[/tex]
