题目: If n is a positive integer and n2 is divisible by 72, then the largest positive integer that must divide n is
选项: (A) 6
(B) 12
(C) 24
(D) 36
(E) 48
Given that 72k = n^2
we must find x such that n|x and n must be the largest one
Since 72 = 2*2*3*3*2
Therefore, we let k = 2, then n = 12, then x = 12 so that it can satisified the largest.