Note that the polynomial $ 9u^2v^4+6uv^2+1 $ is a perfect square trinomial, so we will use the following formula.
$$ A^2 + 2AB + B^2 = (A + B)^2 $$In this example we have $ \color{blue}{ A = 3uv^2 } $ and $ \color{red}{ B = 1 } $ so,
$$ 9u^2v^4+6uv^2+1 = ( \color{blue}{ 3uv^2 } + \color{red}{ 1 } )^2 $$