Maths - Factorizes

1. y^2 + 11y + 18 =
y^2 + 9y + 2y + 18 =
y(y + 9) + 2(y + 9) =
(y + 2)(y + 9)

2. a^2 - b^2 + ay - by =
(a + b)(a - b) + y(a - b) =
(a + y)(a - b)

2006-11-07 17:09:59 補充：
補充:2. a^2 - b^2 + ay - by = (a + b)(a - b) + y(a - b) =(a + b + y)(a - b)

1.y^2+11y+18=
2 y
x
9 y(cross method)
=2y+9y=11y
so the answer is (2+y)(9+y)
2.a^2-b^2+ay-by
=(a+b)(a-b)+y(a-b)then
[by taking out common factor (a-b)]
so the answer =(a-b)(a+b+y)
That's all