To express "a set of positive integers divided by three and remaining one" by descriptive method:______ .

To express "a set of positive integers divided by three and remaining one" by descriptive method:______ .

Solution; ∵ all positive integers divided by 3 and remaining 1 can be written in the form of integral multiple of 3 plus 1, that is, x = 3K + 1, K ∈ n, the description method is used to express the set of positive integers divided by 3 and remaining 1: {x| x = 3K + 1, K ∈ n} so the answer is: {x| x = 3K + 1, K ∈ n}