我要埋式.唔該
更新1:
點解-20會變左做+20既-.-?
F.4 maths題目
2010-01-08 1:06 am
There are two positive numbe. One is 8 greater than the other and the sum of their squares is 544. Fing these two number.
我要埋式.唔該
我要埋式.唔該
回答 (3)
2010-01-08 1:14 am
✔ 最佳答案
Let x be the smaller number, then the larger number is (x+8).x^2 + (x+8)^2 = 544
x^2 + x^2 + 16x + 64 = 544
2x^2 + 16x - 480 = 0
x^2 + 8x - 240 = 0
(x-12)(x+20) = 0
x = 12 or x = -20 (rejected)
The smaller number is 12 and the larger number is 20.
2010-01-07 17:26:01 補充：
the larger number is (12+8) = 20.
2010-01-07 17:26:43 補充：
as we find that smaller number x = 12 => larger number = x+8 = 12+8 = 20.
2010-01-07 17:27:25 補充：
But not -20 changes into 20.
參考: Maths knowledge
2010-01-08 1:15 am
Let one of the number is x, so the other number is (8 + x).
So x^2 + (8 + x)^2 = 544
x^2 + 64 + 16x + x^2 - 544 = 0
2x^2 + 16x - 480 = 0
x^2 + 8x - 240 = 0
(x + 20)(x - 12) = 0
x = - 20 (rej.) or 12.
so the 2 numbers are 12 and 20.
So x^2 + (8 + x)^2 = 544
x^2 + 64 + 16x + x^2 - 544 = 0
2x^2 + 16x - 480 = 0
x^2 + 8x - 240 = 0
(x + 20)(x - 12) = 0
x = - 20 (rej.) or 12.
so the 2 numbers are 12 and 20.
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100107000051KK00840