=[(x+3)(x-3)]?
=(x? -9)?
= x- 18x to the fourth power? +8 1
.
(2)(3m+2n- 1)(3m-2n+ 1)
=[3m+(2n- 1)][3m-(2n- 1)]
=9m? -(2n- 1)?
=9m? -4n? +4n- 1