Question

how do you do 9x^2 -81=0

Answer 1

(3x-9)(3x+9) = 0

Answer 2

how do you dot that? i never learned

Answer 3

It's called difference of squares

Answer 4

If you see nothing but squares and then they are being subtracted, you just use this rule:

ax^2 - b^2 = (ax+b)(ax-b)