1. That original inequality I wrote was completely valid in the first quadrant, but since I want this inequality to be true in the first and fourth quadrants, because I'm taking the limit as x approaches 0 from both sides, I put that absolute value there.

제I사분면에서 아주 잘 성립했어요. 근데 극한에서 x가 0으로 양쪽에서 갈 때를 보니까