viewimage.php?id=3db5c935ecd12bf4&no=24b0d769e1d32ca73deb86fa11d02831d16706cea37200d6da918279867bdc60622bbc9d297149ca105b8af3ded813bfd2cbb9d16647985df11827bfb2922116823c50c8b4677d6b6dfc74eb1f0b4bea1f35faf30975188e31e78ab4cf14f208339426fdd3978775

왜 -2f'(2x)가 아닌지 10분 넘게 생각함