A mathematician couple was having a Frappuccino in Starbucks sitting opposite to each other. Suddenly the guy noticed the text written on the paper in front of them and exclaimed that it was wrong. The girl denied and said it is appropriate. Both are correct. What is written on the paper ?

Mathematician Couple Trick Riddle

The text on the paper was X = XI + 1 which is inaccurate but when read from the girl’s side it becomes I + IX = X which is accurate.