We have
[tex]\mleft(3a-1\mright)^2[/tex]Write as a product is multiply the given binomial the number that we have in the power, in this case, the number of times is 2
The product is
[tex]\mleft(3a-1\mright)^{}\mleft(3a-1\mright)^{}[/tex]Then we need to simplify the product
[tex]9a-3a-3a+1[/tex]Then we sum like terms and we obtain the polynomial
[tex]9a^2-6a+1[/tex]