These math problems are so difficult that they've got me cross-eyed.

cross-eyed 是由形容词 cross（交叉的）和名词 eye（眼睛）加上后缀 -ed 组成的复合形容词。字面意思是"眼睛交叉的"，用来形容因困惑或疲劳导致视线模糊、看东西重影的状态，引申为"晕头转向"的意思。