标题: 数学疑问？ [打印本页] 作者: 麦兜woo 时间: 2010-10-2 10:24 标题: 数学疑问？ 1.The greatest common divisor of a and b is 21, and the least common multiple of a and b is 126, where a and b are positive integers, what is the sum of a and b?
A. 105 B. 147 C.150 D.105or 147 E.105or 150
答案选D，怎么做出来的呢？作者: aaronkib 时间: 2010-10-2 10:33 數學疑問？ 1.The greatest common divisor of a and b is 21, and the least common multiple of a and b is 126, where a and b are positive integers, what is the sum of a and b?
A. 105 B. 147 C.150 D.105or 147 E.105or 150
21=3*7 126=2*3^(2)*7 A,B均含3*7 為滿足the least common multiple of a and b is 126 A, B可為3*7*2, 3*7*3 或是3*7, 2*3^(2)*7