Question

factor each polynomial y²-81

Answer 1

I'm if it's right but.....

you could square root the whole expression and get (y-9)(y-9)=(y-9)^2

Answer 2

y^2-81 is the difference of two squares, namely, the difference of y squared less 9 squared.  Therefore,

y^2-81 = (y-9)(y+9)