The product of two consecutive negative even number is 80. Find the large number .
Let x and x+2 be the two number
計完之後x=8or-10
但點解最後出黎個答案係:
The larger number is -8 -.-?
F.4 maths題目
2010-01-08 1:42 am
回答 (2)
2010-01-08 1:57 am
✔ 最佳答案
Let two consecutive negative even numbers be x and x+2 :then x(x+2) = 80
x^2 + 2x - 80 = 0
(x - 8)(x + 10) = 0
x = 8 (rejected since 8 is not negative number)) or
x = - 10
the larger number = - 10 + 2 = - 8
So the two consecutive negative even number are - 8 and - 10
2010-01-08 2:04 am
呢個問題, 你要睇返條題目, The product of two consecutive negative number is 80.好明顯答案一定要係兩個負數, 姐係 -8 同 -10, 而其中就以-8較大, 所以答案係-8
你可能會有疑問
x(x+2) = 80
x^2 + 2x - 80 = 0
(x-8)(x+10) = 0
x = 8 or x = -10
你可能會問, -8何來?
請睇一睇以下例子:
-(x-8)(x+10) = 0
(x-8)*-(x+10) = 0
以上兩例都同原本一樣的, 因為-1可以除過去0到消去, 由此就可以得到,
其實答案有四個:8,10,-8,-10
而其他兩個正數會被rejected
你可能會有疑問
x(x+2) = 80
x^2 + 2x - 80 = 0
(x-8)(x+10) = 0
x = 8 or x = -10
你可能會問, -8何來?
請睇一睇以下例子:
-(x-8)(x+10) = 0
(x-8)*-(x+10) = 0
以上兩例都同原本一樣的, 因為-1可以除過去0到消去, 由此就可以得到,
其實答案有四個:8,10,-8,-10
而其他兩個正數會被rejected
參考: 自己
收錄日期: 2021-04-21 22:07:28
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100107000051KK00930