21、k 、x、 y、 z 均为正整数，且k=2^ x 3^y 7^z，168与441为k的因子，求x y z？
选项：2 6 8 9 12
the problem might ask which of the 5 choices is possible for x+y+z. Minimum k that satisfies the conditions is (2^7) (3^2) (7^2), so we can get x+y+z>=11. 12 is the only good one.
[此贴子已经被作者于2002-9-13 0:15:05编辑过] | 
