中二數---請有心人幫下我4題數(20點)...

只要答案的看 highlight 的地方吧^^

7. 2 ÷ (t- 2) + [-t ÷(t – 2)]

2 ÷ (t-2) + [-t ÷ (t-2)]

= 2/(t-2) - t/(t-2)

= (2-t)/(t-2)

= -(t-2)/(t-2)

= -1

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8. (2m + n) ÷ m + (m - 3n) ÷ 3m

(2m + n) ÷ m + (m - 3n) ÷ 3m

= (2m + n)/m + (m - 3n) / 3m

= 3(2m + n)/3m + (m - 3n) / 3m

= [3(2m + n) + (m - 3n)] / 3m

= (6m + 3n + m - 3n) / 3m

= 7m / 3m

= 7/3

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9. (2f + g) ÷ (f + 2g) - 2

(2f + g) ÷ (f + 2g) - 2

= (2f + g) / (f + 2g) - 2(f + 2g)/(f + 2g)

= [2f + g - 2(f + 2g)] / (f + 2g)

= (2f + g - 2f - 2g) / (f + 2g)

= -g / (f + 2g)

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我估計你的 2 是指二次方吧？

10. [(3s + 4t) ÷ (9s - 12t)] × (8t - 6s) ÷ [(3s + 4t)^2 ÷ 2]

[(3s + 4t) ÷ (9s - 12t)] × (8t - 6s) ÷ [(3s + 4t)^2 ÷ 2]

= [(3s + 4t) / (9s - 12t)] [(8t - 6s) / [(3s + 4t)^2/2]]

= [(3s + 4t) / 3(3s - 4t)] [-2(3s - 4t) / [(3s + 4t)^2/2]]

= [(3s + 4t) / 3(3s - 4t)] [-4(3s - 4t) / (3s + 4t)^2]

= -4(3s + 4t)(3s - 4t) / 3(3s - 4t)(3s + 4t)^2

= -4/[3(3s + 4t)]

2006-12-29 23:01:16 補充：
如果我的估計錯了，麻煩請告知 ^^

7. 1÷(t-2) × (2-t)

2006-12-29 23:01:37 補充：
8.7/3

2006-12-29 23:07:55 補充：
9. -1