$(4a+1)(4a-1) $= ? Please write a polynomial

Question

$(4a+1)(4a-1) =$ ? The main thing is write is polynomial. My answer is: $16a^2-1$ but not sure.

Answer 1

$16a^2 - 1$ is a polynomial (in $a$), so that's the correct answer.

Answer 2

$(4a +1)(4a -1) = 16a^2 -4a +4a -1 = 16a^2 -1$, which is a polynomial in a (think $a$ as $x$ and it will look like as usual)

Answer 3

In general $(x-b)(x+b)=x^2-b^2$

In this case $x=4a$ and $b=1$