初中數學,唔識做... (2)

6. [(ab)/(a-b)] / [(a2)/(b-a)]
= (ab)/(a-b) x (b-a)/(a2)
= b/-(b-a) x (b-a)/a…………約分
= (b/-1) x (1/a)………………再約分
= -b/a //

7. 2/(3x) – 3/(2x)
= 4/(6x) – 9/(6x)………….通分
= (4-9)/(6x)
= -5/(6x) //

8. b/[4(2a-b)] – 2/[3(2a-b)]
= 3b/[12(2a-b)] – 8/[12(2a-b)]………….. 通分
= (3b-8)/[12(2a-b)]

9. 5/[3(a-b)] + 7/[6(b-a)]
= 10/[6(a-b)] – 7/[6(a-b)]………….通分&把(b-a)轉為 -(a-b)
= (10-7)/[6(a-b)]
= 3/[6(a-b)]
= 1/[2(a-b)] //……………約分

10. 1–1/(x+1)
=(x+1)/(x+1) – 1/(x+1)……….. 通分
=(x+1-1)/(x+1)
=x/(x+1) //

2007-01-02 14:20:54 補充：
sorry, no.6內的指數符號錯左, 應該係:6. [(ab)/(a-b)] / [(a²)/(b-a)]= (ab)/(a-b) x (b-a)/(a²)= b/-(b-a) x (b-a)/a…………約分= (b/-1) x (1/a)………………再約分= -b/a //

2007-01-02 14:28:29 補充：
小提示:上面有D朋友個答案計錯左~ 同埋計親呢D algebraic fraction的加減的時候, 個答案唔洗expand左佢(e.g. 第8題個答案可以係 (3b-8)/[12(2a-b)] 或 (3b-8)/(24a-12b) , 不過通常都係唔會約的, 因為條問題的重點唔係考你識唔識expand D分數, 而係考你識唔識通分, 約分和 "轉符號")

6. (ab)/(a-b) ÷ (a^2)/(b-a)
= (ab)/(a-b) × (b-a)/(a^2) ← ÷號變×號，分子分母顛倒
= (ab)/(a-b) × [-(a-b)/(a^2)] ←把(b-a)變成-(a-b)
= -(ab)/(a^2) ←便可把前一項的分母(a-b)約去
= -b/a∥ ←約走分子的a和分母的a^2中的a後，便剩下分母的a

7. 看不到題目

8. b/[4(2a-b]) - 2/[3(2a-b)]
= (3b)/[12(2a-b)] - (2×4)/[12(2a-b)] ←通分母
= (3b-8)/[12(2a-b)]
= (3b-8)/(24a-12b)∥

9. 看不到題目

10. 1 - 1/(x+1)
= (x+1)/(x+1) - 1/(x+1) ←通分母
= (x+1-1)/(x+1)
= x/(x+1)∥

另：你的字體寫得很美

6.b/a-b*b-a/a
=b/a-b*-(-b+a/a)
=b*-a
=-ab

7.2/3x-3/2x
=4/6x-9/6x
=4-9/6x
=-5x

2007-01-02 13:29:37 補充：
9.5/3(a-b) 7/6(b-a)=10/6(a-b) 7/-6(-b a)=-(10-7)/6(a-b)=-3/6(a-b)=-1/2(a-b)10.1-1/x 1=x 1/x 1-1/x 1=x 1-1/x 1-x 1=x/x-x 1 1=x/2

2007-01-02 13:31:28 補充：
Sorry,第8題唔識做