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题库 / Prep2007E2-DS-32
Is positive integer n divisible by 3 ?
(1) ~$\frac{n^{2}}{36}$~ is an integer.
(2) ~$\frac{144}{n^{2}}$~ is an integer.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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注意条件已经shuole3n是一个整数！！！
条件一·(n^2)/36=（n/6）^2=（n/2·3）^2=整数
说明n一定包含2和3两个·因子，所以1充分
条件二·144/(n^2)=（12/n）^2=（2·2·3/n）^2=整数
说明只要n包含2或3就可以成立，所以2不充分
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