20分!!升中三數(急急急!!!!!!!!!!!)

恆等:證明是否恆等:-3x(x-4)=-3x2次-12x

左方=-3X^2+12X
右方=-3X^2-12X
左方=右方
所以:-3x(x-4)=-3x2次-12x是恆等式.


1:Ax+B恆等7x-4
A=7,B=-4
2:(A-B)x+B恆等8x-5
A=3,B=-5

6a+24b
=6(a+4b)

ab+ac+bd+cd
=a(b+c)+d(b+c)
=(a+d)(b+c)

x2次+6x+9
=(x+3)^2

x2次-6x+9
=(x-3)^2

x2次-64
=(x+8)(x-8)

四捨5入:(準至3位數):3.63414
=3.63(correct to 3 sig. fig.)

比與率:化简:9:6
=3:2

0.25:0.75
=1:3

-3x(x-4)
= -3x^2 + 12x which is different from -3x^2-12x ...

1. Ax + B = 7x - 4 .......hence A=7 & B=-4
2. (A - B)x + B = 8x - 5 ........ hence A - B = 8 & B = -5
Thus, B = -5 & A = 8 + B = 8 - 5 = 3

6a + 24b = 6 (a + 4b)

ab + ac + bd + cd
= ab + bd + ac + cd
= b (a + d) + c (a + d)
= (b + c)(a + d)

x^2 + 6x + 9 = (x + 3)^2

x^2 - 6x + 9 = (x - 3)^2

x^2 - 64 = x^2 - 8^2 = (x - 8)(x + 8)

3.63414 ~ 3.63 corr to 3 sig fig (準至3個位)

9:6 = 3:2

0.25: 0.75 = 25:75 = 5:12

2007-08-28 21:08:40 補充：
sorry! 0.25:0.75 = 25:75 = 1:3

L.H.S = -3x(x-4)
= -3x^2 +12x
R.H.S = -3x^2 -12x
L.H.S 不等於R.H.S
所以3x(x-4)=-3x2次-12x不是恆等

1) A=7, B=-4
2) B=-5, A-B =8 --> A-(-5) =8 --> A+5=8--> A=3

6a +24b = 6(a+4b)

ab+ac+bd+cd =a(b+c) +d(b+c) =(a+d)(b+c)

x^2+6x+9 = (x+3)^2

x^2-6x+9=(x-3)^2

x^2 -64 = (x+8)(x-8)

3四捨5入:(準至3位數):3.63414???有冇打錯..
如果三位有效數 = 3.63

9:6 = 3:2
0.25:0.75 = 1:3

證明是否恆等:-3x(x-4) = -3x^2-12x
左邊 = -3x(x-4) = -3x^2+12x 唔等於右邊
所以不是恆等
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求以下2個含x的恆等中的A和B:
1:Ax+B恆等7x-4
當 x = 0, B = -4
當 x = 1, A+B = 7-4 = 3
A+(-4) = 3, A = 7
-------------------------------------------------------
2:(A-B)x+B恆等8x-5
當 x = 0, B = -5
當 x = 1, A-B+B = A = 8-5 = 3
-------------------------------------------------------

因式分解:
6a+24b = 6(a+4b)
ab+ac+bd+cd = a(b+c)+d(b+c) = (a+d)(b+c)
x^2+6x+9 = (x+3)^2
x^2-6x+9 = (x-3)^2
x^2-64 = x^2-8^2 = (x+8)(x-8)
x^2-64 = (x+8)(x-8)
-------------------------------------------------------

四捨5入:(準至3位數):
3.63414 = 3.63

-------------------------------------------------------

比與率:化简:
9:6 = 3:2
0.25:0.75 = 25:75 = 1:3

2007-08-28 21:00:11 補充：
慢左, 不過上面位人兄 <恆等證明> 果度有少少錯多多支持