3題數學題...唔識做!!help!!明天交...!!!

1a) A=(x+x+6)(9-x)/2

1b) 20=(x+x+6)(9-x)/2
20=-x^2+6x+27
x^2-6x-7=0
(x-7)(x+1)=0
x=7 or x=-1

2a) 3=3(1)^2+b(1)+c
b+c=0
b=-c------------(1)
3=3(2)^2+b(2)+c
2b+c=-9--------(2)
Put (1) into (2)
2(-c)+c=-9
c=9
Put c=9 into (1)
b=-9
Thus, b=-9, c=9.

2b) I'm sorry, I don't know.

3) (2k-1)^2-(4)(k+1)(k+2)<0
4k^2-4k+1-4k^2-12k-8<0
-16k-7<0
-16k<7
k>7/-16

1.a. (x+x+6) x (9-x)/2
=(18x-2x^2+54-6x)/2
=2(9x-x62+27-3x)/2
=-x^2+6x+27

1.b. -x^2+6x+27=20
-x^2+6x+7=0
(x+1)(7-x)=0
x=-1,x=7
3) (2k-1)^2-(4)(k+1)(k+2)<0
4k^2-4k+1-4k^2-12k-8<0
-16k-7<0
-16k<7
k>7/-16

1.a. (x+x+6) x (9-x)/2
=(18x-2x^2+54-6x)/2
=2(9x-x62+27-3x)/2
=-x^2+6x+27

1.b. -x^2+6x+27=20
-x^2+6x+7=0
(x+1)(7-x)=0
x=-1,x=7

* ^即係次方,x^2即係x ge2次方

2008-11-09 14:26:34 補充：
2.b. b^2-4ac
=(-9)^2-4(3)(9)
=-27
所以,no any x intercept
希望幫到你啦,
我覺得你同我個fd個名好似,
唔知你係唔係我fd呢@@

雖然我好想幫你,但我唔識,sorry