請問呢幾題點樣因式分解?????

1. x^2-9+(x-3)(x+4)
= (x-3)(x+3) + (x-3)(x+4)
= (x-3)(2x+7)


2.2ab-a^2-b^2
= - (a2 - 2ab + b2)
= - (a + b)2



3.16a^2-24ab+9b^2
= (4a - 3b)2


4.6x^2+xy-12y^2
= (3x + 4y)(2x - 3y)


5.(a^2+4a+4)-(b^2-2b+1)
= (a+2)2 - (b-1)2
= (a+b+1)(a-b+3)

1.
x^2-9 + (x-3)(x+4)
= (x-3)(x+3) + (x-3)(x+4) = (x-3)[(x+3) + (x+4)] = (x-3)(2x +7).
2.
2ab - a^2 - b^2 = -(a^2 -2ab + b^2) = -(a-b)^2.
3.
16a^2 - 24ab + 9b^2 = (4a)^2 - 24ab + (3b)^2 = (4a - 3b)^2.
4.
6x^2 + xy - 12y^2 = (3x - 4y)(2x + 3y) . (Hint: 6 = 3 x 2 and 12 = 3 x 4)
5.
(a^2 + 4a + 4) - (b^2 - 2b + 1) = (a+2)^2 - (b-1)^2 = [(a+2) + (b-1)][(a+2) - (b-1)] = (a + b +1 )(a - b + 3).