maths~~~~~~

I will do 17a and 17b
(a)
P(x+1)(x+2)+Q(x+2)(x+3)+R(x+3)(x+4)≡x²+8x+14
P(x²+3x+2)+Q(x²+5x+6)+R(x²+7x+12)≡x²+8x+14
Px²+Qx²+Rx²+3Px+5Qx+7Rx+2P+6Q+12R≡x²+8x+14
(P+Q+R)x²+(3P+5Q+7R)x+(2P+6Q+12R)≡x²+8x+14
Hence,
P+Q+R=1---(1)
3P+5Q+7R=8---(2)
2P+6Q+12R=14---(3)
From (3), P+3Q+6R=7---(4)
(4)-(1):
2Q+5R=6---(5)
(2)-(1)x3:
2Q+4R=5---(6)
(5)-(6):
R=1---(7)
Sub (7) into (5):
2Q+5(1)=6
Q=0.5---(8)
Sub (7) and (8) into (1):
P+1+0.5=1
P=-0.5
Therefore
P=-0.5,Q=0.5,R=1
(b)
-2(x+1)(x+2)+2(x+2)(x+3)+4(x+3)(x+4)=3x²+20x+29
(-2+2+4)x²+[3(-2)+5(2)+7(4)]x+[2(-2)+6(2)+12(4)]=3x²+20x+29
4x²+32x+56=3x²+20x+29
x²+12x+27=0
(x+3)(x+9)=0
x=-3 or x=-9

-2(x+1)(x+2)+2(x+2)(x+3)+4(x+3)(x+4)=3x^2+20x+29
-2x^2-4+2x^2+12+4x^2+48=3x^2+20x+29
(-2x^2+2x^2)+4x^2+56=3x^2+20x+29
4x^2-3x^2+56-29=20x
x^2+27=20x
x^2/20x=-27
x/20=-27
x=-540

2007-03-20 23:26:35 補充：
I just F.1.

其實都係拆開佢然後合番埋佢，都唔知點打俾你，答案是 -3 或 -9。

2007-03-20 22:03:07 補充：
其實17A你都無問題，無理由唔識做17B。