F.3 Mathematics

1. 9a^2-b^2-12a-4b
= 9a^2 - b^2 - 4(3a+b)
= (3a+b) (3a-b) - 4(3a+b)
= (3a+b) (3a-b-4)

2. x^2-7x-30
= (x+3) (x-10)

3. 18x^2-4-x
= (9x+4) (2x-1)

4. x^2y^2-x^2-2x-1
= x^2y^2 - (x^2+2x+1)
= x^2y^2 - (x+1)^2
= (x^2y+x+1) (x^2y-x-1)

5. a^6-8b^6
= (a^2)^3 - (2b^2)^3
= (a^2-2b^2) (a^4 - 2 a^2 b^2 + 4b^4)

唔明可以再黎搵我 ：）