Simple,
distribute the \(^{2}\)
It may seem tricky..there is a hidden term in there that most people would forget....
but, it's saying multiply (a-3b)(a-3b) (FOIL)
aa=\(a^{2}\) (First)
-3ba= -3ab (Outer)
-3ba= -3ab (Inner)
-3b-3b= 9\(b^{2}\) (Last)
Making it....
\(a^{2}+-3ab+-3ab+9 b^{2}\)
Combine terms...
Making your answer, \(a^{2} -6ab+9 b^{2}\)
