中四附加數學

y = (x^2 - x + 7) / (x + 1)
(x+1)y= (x^2 - x + 7)
0=x^2-x+7-xy-y
0=x^2-(1+y)x+7-y
because x is real, so D>=0
(1-y)^2-4(7+y)(1)>=0
1-2y+y^2-28-4y>=0
y^2-6y-27>=0
(y-9)(y+3)>=0
y<=-3 or y>=9
x is real指 Delta 大過等於0

2007-12-30 07:25:58 補充：
有些少計錯,更正如下(1 y)^2-4(7-y)(1) =01 2y y^2-28 4y =0y^2 6y-27 =0(y 9)(y-3) =0y =3

2007-12-30 07:27:14 補充：
(1 y)2 -4(7-y)(1)≧01 2y y^2-28 4y≧0y^2 6y-27≧0(y 9)(y-3)≧0Y≦-9 or y≧3

x is real 代表x 是實數. 中四開始, 會引入所謂 imaginary numbers
既概念(唔知你學到未?). 簡單來說 imaginary numbers 包含一個
imaginary part (i) = 開方 -1. 而你以前學的 maths中, 負數是不能
開方的, 當一個有√-1 出現時, 就叫 imaginary numbers(虛數),
而與此相反, 沒有√-1的數, 就是real numbers(實數).

X 係實數 ...姐係 佢係有得計
但係呢條數 好似無得計WOR....

2007-12-29 18:55:08 補充：
y = (x2 - x 7) / (x 1)(x 1)y= (x2 - x 7)0=x2-x 7-xy-y0=x2-(1 y)x 7-ybecause x is real, so △≧0(1-y)2 -4(7 y)(1)≧01-2y y^2-28-4y≧0y^2-6y-27≧0(y-9)(y 3)≧0Y≦-3 or y≧9