To factorize the given function you:
You can find if the equation correspond to a perfect square trinomial by knowing that the numbers 16x^2 and 25 are perfect squares (numbers that have a perfect sqare root) and the term 40x is equal to 2 times 4x*5. and 5.
Then,
[tex]\begin{gathered} 16x^2=(4x)^2 \\ 25=5^2 \\ 40x=2(4x)^{}(5) \end{gathered}[/tex]The equation follows the next general form to a perfect square trinomial:
[tex]a^2+2ab+b^2[/tex]Then, you can rewrite the given equation as:
[tex](4x)^2+2(5)(4x)+5^2[/tex]And knowing that:
[tex]a^2+2ab+b^2=(a+b)^2[/tex]You get that the given equation is equal to:
[tex](4x+5)^2[/tex]