=[(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