F.2數學題1條 (10分!!!!!!!!!)

(12x+4)(Ax-2)≣ 6x²+Bx+C
12Ax²+4Ax-12x-6=6x²+Bx+C


A=1/2 B=4(1/2)-12 C=-6

起碼幫到你啦

2008-01-25 00:23:06 補充：
c係-8先o岩乘錯數xd

2008-01-25 00:26:08 補充：
對唔住乖錯左數=.=你跟二樓個哥哥啦,佢解釋得比較清淅同埋起碼唔似我咁計錯數

展開(12x+4)(Ax-2)
(12x+4)(Ax-2)=12Ax²-24x+4Ax-8
=12Ax²-(24-4A)x-8
因為左面=右面
12Ax²-(24-4A)x-8 ≣ 6x²+Bx+C
所以
12Ax²=6x²
12A=6
A=1/2

-(24-4A)x=Bx
-24+4A=B <---------代A=1/2入去
-24+4(1/2)=B
-24+2=B
B=-22

所以A=1/2 B=-22 C=-8

(12x+4)(Ax-2)≣ 6x²+Bx+C
L.H.S.=((12x+4)(Ax-2)
=12Ax²+4Ax-24x-8
=12Ax²+x(4A-24)-8
∵(12x+4)(Ax-2)≣ 6x²+Bx+C,
∴By comparing the coeffient of the like terms：12A=6
A=6/12
A=1/2〃
B=4A-24
B=4(1/2)-24
B=2-24
B=-22〃

左方=12Ax^2-(24-4A)x-8

即12Ax^2=6x^2
12A=6
A=1/2

(24-4A)x=Bx
代A=1/2 (24-2)x=Bx
22=B

(12x+4)(Ax-2) ≣ 6x²+Bx+C
L.H.S=(12x+4)(Ax-2)
12Ax²+4Ax-12x-8
12Ax²+x(4A+12)-8
R.H.S=6x²+Bx+C

by comparing like terms,
A=1/2 B=4*1/2+12
=14

If (12x+4)(Ax-2) ≣ 6x²+Bx+C, find A,B.

first, expand (12x+4)(Ax-2) ,
LHS=(12x+4)(Ax-2)
=12Ax²+4Ax-24x-8
=12Ax²+(2A-24)x-8
due to LHS=RHS
so, 12Ax²+(2A-24)x-8=6x²+Bx+C,

no we can find that 12A=6,2A-24=B, -8=C

so,A=1/2, B=12(1/2)-24=-18

then we can find out the answer quickly~^^

(12x+4)(Ax-2)
=12Ax^2 - 24x+4Ax-8
12Ax^2 -(24+4A)x - 8 = 6x^2+Bx+C

Then, 12Ax^2 = 6x^2
12A = 6
A = 0.5

-(24+4A) = B
-(24 +2) = B
B = -26

C = -8

2008-01-24 18:58:58 補充：
Sorry, did one thing wrong. it should be -(24 - 4A) =B , so B = -22

(12x+4)(Ax-2) ≣ 6x²+Bx+C
L.H.S= 12Ax² +4Ax-24x-8
R.H.S=6x²+Bx+C
By comparing like terms, we have
12A=6
A=1/2
B=4A-24
= -22
C= -8

2008-01-24 18:57:37 補充：
與stlouisschool2002
的答法大同小異,用邊個都得