招人教我F.2數學,要列式+解說;(

1.pq-4q+3p-12
=(pq-4q)+(3q-12) (<一組組睇啦)
=q(p-4)+3(p-4) (<抽佢地個common factor出黎;第1組係q嘛,第2組係4)
=(p-4)(q+3) (<上面既第1,2組都有p-4所以就可以抽出黎)

2. 7x²+5xy-18y²
呢類型既數有2種計法,而家只可以用cross method,第2種我一陣再教你
cross method即係交叉相乘,拎頭尾2個(即 7x²同18y²)(7只可以7x1/18可以9x2同6x3)
7x -9y
x +2y
----------------- (*<乘個陣要交叉乘,寫要打橫寫)
+14xy-9xy

7x²+5xy-18y²
=(7x-9y)(x+2y)


6x² x-y
— x —
x²-y² 2x
(乘要交叉相乘,記得嗎?先望望6x²同2x,6x²約到2x,再睇下x²-y²同x-y,x²-y²約到x-y)
3x
=—
x-y


教住咁多先,你睇下有咩唔明,你有咩唔明可以問我,其他我打緊....

2012-08-14 22:03:46 補充：
４.If (x+3)(2x-5)+C=Ax²+(A+B)x-9, where A, B and C are constants. Find the values of ,B and C. (我知唔係每個人都讀英中,識就答;) )
(x+3)(2x-5)+C=Ax²+(A+B)x-9 (<首先將(x+3)(2x-5)乘左佢)
2x²-5x+6x-15+C=Ax²+(A+B)x-9 (<見唔見到l.h.s同r.h.s既第1項2x²同Ax²,大家都係x²,所以..)
A=2
之後我就唔識啦sorry..=[

2012-08-14 22:04:13 補充：
5.Consider the formula y-2x=3(xy+1).

(a.) Make y the subject of the formula.
y-2x=3(xy+1)
y-2x=3(xy+1) (<首先將3乘入去)
y-3xy=3+2x (<因為你要抽個y出黎,所以將所有有y既掉哂去l.h.s)
y(1-3x)=3+2x (<抽個y出黎)
3+2x
y=— — (<掉過去記住埋下面牙;))
1-3x

2012-08-14 22:04:33 補充：
(b.) Find the value of y when x = 二分一
3+2x
y=— — (<用番頭先個個答案)
1-3x

3+2(1/2)
y=— — — (<將1/2套入x就ok)
1-3(1/2)


3+1
y=— —
1-1.5

4
y=- — = - 8
0.5

2012-08-14 22:04:51 補充：
6.
2 3x
—— - ———— (<望下第2組數既分母,仲記唔記得佢牙?;)呢個都要用cross method的)
x+2 2x²+5x+2

2x +1
x +2
------------- (打橫寫牙記唔記得牙?;))
+4x+x=5x

2 3x
= —— - —————
x+2 (2x+1)(x+2)

之後又唔識了....唔好意思^^"

2012-08-14 22:20:02 補充：
７. Class mark 、 Frequcncy點解?
class mark 即係組中點....即係一組數褢面既中間數....
一個histogram咪有數字既~~
例如:一班女仔既身高係140-144cm/145-159cm/160-164cm/165-169cm
class mark即係:(140+144)除2=142cm

2012-08-14 22:20:15 補充：
frequency咪即係第1第2題囉~~
記唔記得我同你講做frequency有2個method既~~
例如:4x²+12xy+9y²
=(2x)²+12xy+(3y)² (<因為4同9都可以開方)
=(2x)²+2(2x)(3y)+(3y)² (<中間一定要乘2,再將左右唔包²個個數乘入去,加出黎等於中間本身個個數)
=(2x+3y)²

Question (1) and (2) 是否 Factorize?

１.
pq-4q+3p-12=?
(pq-4q)+(3p-12)
q(p-4) +3(p - 4)
(q + 3) (p – 4)

２.
7x²+5xy-18y²=?
(7x-9y)(x + 2y)

3.
6x² x-y
—--- x —---- =?
x²-y² 2x

6x² (x-y)
—----------- x —---- =?
(x+y)(x-y) 2x

3x
--------
(x + y)


４.
If (x+3)(2x-5)+C=Ax²+(A+B)x-9, where A, B and C are constants. Find the values of ,B and C.
2x^2 +x – 15 + C = Ax²+(A+B)x-9
2x^2 +x – (15 – C) = Ax²+(A+B)x-9
A = 2
(A+ B) = 1
2 + B = 1
B =1 – 2
B = -1
15 – C = 9
C =15 – 9 = 6
A = 2, B = -1, C = 6

５.
Consider the formula y-2x=3(xy+1).
(a.) Make y the subject of the formula.
y-2x =3(xy+1)
y-2x =3xy + 3
y – 3xy = 2x + 3
y(1 – 3x) = 2x + 3
y = (2x + 3)/(1 – 3x)

(b.) Find the value of y when x = 二分一
y = (2x + 3)/(1 – 3x)
y = (2(0.5) + 3)/(1 – 3(0.5))
y = (1 + 3)/(1 – 1.5)
y = 4/-0.5
y = -8

6.
2 3x
----- - ----------- =?
x+2 2x²+5x+2

2 3x
—---- - —-------------- =?
(x+2) (2x+1)(x+2)

2 (2x +1) 3x
—------------- - —-------------- =?
(x+2)(2x +1) (2x+1)(x+2)

2 (2x +1) - 3x
—------------- — =?
(x+2)(2x +1)

4x +2 - 3x
—------------- — =?
(x+2)(2x +1)

(x +2)
—------------- — =?
(x+2)(2x +1)

1
—-------
(2x +1)


７. Class mark 、 Frequcncy點解?

Frequency = the number of times that something happens within a particular period of time or within a particular group of people
(簡單地, Frequency is the number of times that an event has taken place)

Frequency is number of cycles per unit time. (Physics)


2012-08-07 07:16:10 補充：
frequency = 發生次數;
frequency = 頻率(sound, electricity)

你要識 Factorization
x^2 - y^2 = (x + y)(x - y) Diffeence of squares
x^2 + 2xy + y^2 = (x + y)^2
x^2 +- 2xy + y^2 = (x - y)^2