中四數學 關於化簡

Question. 3
Using sine law
x/sin 64°
x/0.8988 = (x+ 1)/0.9455
0.9455x = 0.8988 (x+ 1)
0.9455x = 0.8988 x+ 0.8988
0.9455x - 0.8988 x = 0.8988
0.0467x = 0.8988
x = 19.246

Question. 14
(a^3 – 27)/(2a^2 – 18)
(a^3 – 3^3)/[(2(a^2 – 3^2)]
(a-3)(a^2 + 3a +9)/2(a+3)(a-3)
(a^2 + 3a +9)/[2(a+3)]

Question 16.
(a)
(x^4 – 81)/(x^2 – 9)
[(x^2)^2 – 9^2]/(x^2 – 9)
(x^2 + 9) (x^2 – 9)/(x^2 – 9)
x^2 + 9

(b)
(6x^4 – 36y^2)/ ( x^4 +6x^2y + 9y^2)
6(x^4 – 6y^2)/[(x^2 + 3y)(x^2 + 3y)]

Question 42.
(1/x –x^2) / (x – 1/x)
(1/x –x^3/x) / (x^2/x – 1/x)
[(1 –x^3)/x] /[ (x^2 – 1) /x]
[(1 –x^3)/x] x /[ (x^2 – 1)]
[(1 –x)(1 +x + x^2)]/[(x+1)(x-1)]
-(1 +x + x^2)/(x+1)
-(x^2 +x +1)/(x+1)

Question 27.
a + 2 -2b –ab b^2-4b-5
-------------------- 除 -----------------
a^2+2a 4-4b^2

(a + 2) –b(2 +a) (b-5)(b +1)
---------------------- 除 -----------------
a(a+2) 4(1- b^2)

(1- b)(a + 2) (b-5)(b +1)
----------------- 除 -----------------
a(a+2) 4(1+ b)(1-b)

(1- b) (b-5)
----------- 除 -----------------
a 4 (1-b)

(1- b ) 4 (1-b)
----------- 乘 -----------------
a (b-5)

4(1-b)^2
------------
a(b – 5)

2011-06-08 02:13:14 補充：
Correction: unit is missing
Question 3:
x = 19.246 cm

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http://img863.imageshack.us/img863/4986/img614q.jpg

試下

2011-06-08 00:16:56 補充：
放唔倒相 咁樣你應該會明

a+2 - 2b -a b / a^2 + 2a ÷ b^2 - 4b - 5 / 4 - 4b^2

/係分子分母

答案係
4(1-b)^2/a(b-5)

plz show no.27 photo~~~thx