F.3 math (20分) 急!!!

唔打問題~
1)
1^2 -(a-b)^2
=(1-a-b)(1+a-b) <---睇番恆等式
2)
個answer係咪計a???(諗倒答你)

3)let 丙 be 1,乙 be (1-10%) ,甲be 120% x(1-10%)
120% x(1-10%)
=108%
because
丙 is 1(100%)
hence, 108%-100%=8%

4)化做:\
1/(a^2) =4
4a^2 = 1
a ^2 = 1/4
a =+ - 1/2

5)(諗倒答你)

2007-01-23 20:02:28 補充：
第5題answer係X=1嗎??如果唔係,sorry la,只可解答們3題

2007-01-23 20:07:39 補充：
其實第5題個問題係唔係 X(2^x) 2 ^(x 1) -2X-4 = 0

2007-01-23 20:08:34 補充：
X(2^x) 2 ^(x -1) -2X-4 = 0 (更正)

2: Method 1
As 2 is the root, subs. 2 into the Equation
2(2)^2 + a(2) - 4 =0
a= -2
equation : 2x^2 -2x -4 = 0 ==> x^2 - x - 2 = 0
Root are 2 and -1

Method 2: product of roots of equation ax^2+bx+c = c/a
let the other root be r, r*2 = -4/2 ==> r = -1