https://www.syu.ac.kr/blog/%eb%8c%80%ed%95%99%ec%9b%90-%ec%a1%b0%ea%b5%90-%ec%b1%84%ec%9a%a9-%ea%b3%b5%ea%b3%a0-2/%e1%84%89%e1%85%a1%e1%86%b7%e1%84%8b%e1%85%b2%e1%86%a8%e1%84%83%e1%85%a2%e1%84%92%e1%85%a1%e1%86%a8%e1%84%80%e1%85%ad%e1%84%8b%e1%85%b5%e1%86%b8%e1%84%89%e1%85%a1%e1%84%8c%e1%85%b5%e1%84%8b%e1%85%af-6/