Question

factorise the following
1)x²-y²upon9

Answer 1

Take square in out of bracket. So it will be in a minus b whole square formulae.
The formula is a square + b square - 2ab

Answer 2

(x²-y²)/9=x²/9-y²/9=(x/3)²-(y/3)²=(x/3+y/3)(x/3-y/3)