Re: [機經] 數學JJ 請解惑
試試看.
有誤請見諒.
※ 引述《waterdrop (林)》之銘言：
: 230. n是否為質數？
: (1)n的質數都比n開三次方小
: (2)n的質數都比n開二次方小
^^^^應為質因數
多謝眾位提醒..
的確.只要是質數.都不符合1 & 2.
所以任何符合1 或 2的.必不是質數.
=> D
: 236. 已知N>1, N是不是prime number感覺比較糾結的題目是這道
: (1)n的任何prime factor都大于n^1/3
: (2)n的任何prime factor都大于n^1/2
感謝E大提醒.
1) Fn^3 > N
a. N is a prime number, Fn = N, (1) is satisfied.
b. N is not a prime number, consider
i. N = 2 * 2 = 4, 2^3 > 2 * 2, (1) is satisfied.
ii. N = 2 * 5 = 10, 2^3 < 10, (1) is not satisfied.
=> statement is not sufficient.
2) Fn^2 > N
a. N is a prime number, Fn = N, (2) is satisfied.
b. N is not a prime number,
N = Fn1 * Fn2, if Fn1 < Fn2
then Fn1^2 < N, (2) is not satisfied.
=> statement is sufficient.
=> B
: -------------------------------
: 231. 0<x<y, 問x<10?
: (1)1/x+1/y=1/5
: (2)1/x>10
: D
: -------------------------------
0 < x < y => 1/x > 1/y
1) 1/x + 1/x > 1/x + 1/y = 1/5
=> 1/x > 1/10
=> X < 10
2) 1/x > 10
=> x < 1/10 < 10
=> D
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◆ From: 61.64.190.248
推
10/27 21:44, , 1F
10/27 21:44, 1F
多謝提醒..不過1不行..
※ 編輯: sausageL 來自: 61.64.190.248 (10/27 22:29)
推
10/27 21:55, , 2F
10/27 21:55, 2F
→
10/27 21:56, , 3F
10/27 21:56, 3F
→
10/27 22:35, , 4F
10/27 22:35, 4F
推
10/28 00:17, , 5F
10/28 00:17, 5F
雖然質數必滿足條件1.但非質數亦有可能滿足.
故條件1不足以判斷N是否為質數.
推
10/28 15:44, , 6F
10/28 15:44, 6F
感謝.
※ 編輯: sausageL 來自: 61.64.190.225 (10/29 00:39)
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